Middle Vessel Batch Distillation Research Articles

Batch distillation performance improvement through vessel holdup redistribution—Insights from two case studies

Middle vessel batch distillation (MVBD) is an energy-efficient configuration for separation of a ternary mixture. This paper focuses on improving the performance of this configuration through dynamic optimization of vessel holdup. Initially, a performance measure accounting for separation and energy efficiency is defined to characterize an operational policy. Subsequently, this measure is maximized by dynamically redistributing holdup in the three (top, middle and bottom) vessels. With the help of two case studies, the impact of various policy decisions and market conditions (such as initial feed distribution and relative cost of products and energy) on the optimal operating policy is analyzed. Specifically, the improvement obtained via holdup redistribution is explained with the help of fundamental concepts of distillation. Lastly, the performance of the proposed approach is compared with some of the existing methods and validated through rigorous simulations.

A hybrid batch distillation/membrane process for high purification part 2: Removing of heavy impurities from xenon extracted from natural gas

High-purity xenon of 6 N purity grade and higher is widely used in electronics, space, and medicine. A hybrid distillation/membrane process for the purification of xenon extracted from natural gas by gas hydrate crystallization is studied experimentally and via simulations. Membrane gas separation data for xenon-containing mixtures is measured for polysulfone membrane and polyetherimide/polyimide blend membrane. Parametric analysis and process optimization are performed in Aspen Plus Dynamics™ for a middle-vessel batch distillation column with an integrated hollow fiber membrane unit implemented via Aspen Custom Modeler™. Removal of higher- and lower-boiling impurities such as ethane, carbon dioxide, propane, methane, and krypton is considered to achieve 6 N and 9 N target purity grades. Hybrid distillation/membrane process flowsheets built with a multi-stream passive heat exchanger with either retentate or permeate being returned to the column are analysed. It is shown that the operating conditions and the configuration of the hybrid process with a membrane separation treatment of heavy impurities fraction can be tailored to achieve up to 30% increase in batch productivity for the considered case studies and improve xenon recovery reaching above 99.8% as compared to standalone batch distillation, which is especially critical for higher purity grades.

Simultaneous separation of ternary mixture using modified dual compression middle vessel batch distillation column: Control and dynamic optimization

BackgroundMultivessel batch distillation has been found to be an effective method for the separation of multi-component mixtures. In this article, an effort has been made to devise a fast middle vessel batch distillation column (MVBDC) for the ternary separation of an Ethanol/Propanol/Butanol mixture by the means of inducing vapor compression in the system. MethodsASPEN PLUS V12 has been used to generate the initial steady-state flowsheet of the process for equipment sizing. In contrast, ASPEN Dynamics was used to evaluate the performance of the batch distillation with various control structures and to perform a dynamic optimization on the proposed batch distillation column. MATLAB was used to identify single-input single-output transfer functions for more effective PID controller tuning. Significant FindingsThe proposed Middle vessel batch distillation was found to separate each component of the mixture to a purity of 99 mol% in 22 h (for the cascade control structures) and 21.73 h (for the temperature control structure). This was found to be significantly lesser than the batch time of a conventional batch distillation column (28.12 h), while the energy consumed by the proposed column was 3.4 MMkcal lesser than the energy consumed by the conventional column. Dynamic optimization further reduced the batch time by 14.4% while simultaneously reducing the energy consumed by 20.3%.

Control and dynamic optimization of middle vessel batch distillation column for the separation of ethanol/propanol/butanol mixture

The middle vessel batch distillation column is an alternative to the regular batch distillation column. This configuration allows simultaneous separation of the light fraction (accumulated at top), heavy fraction (accumulated at bottom) and the intermediate fraction (accumulated in the middle vessel) in a single column. The objective of this article is to extensively analyse and discuss different control systems for the middle vessel batch distillation column (MVBDC) and dynamically optimize the column. Three control structures such as composition level cascade, composition temperature cascade, and temperature control system, have been tested and evaluated. Further, a dynamic optimization study has been performed on the control system providing the fastest separation. The optimizer is set to minimize the total energy consumed during the process. This resulted in a decrease in batch time from 26.8 to 25.2h and a 13.5% decrease in overall energy usage. The presented dynamic optimization technique and control system design is useful for improving the performance of the MVBDC.

Dynamic performance comparison of two configurations of middle vessel batch distillation column for the separation of ethanol/propanol/butanol mixture

AbstractThis paper deals with Aspen Plus and Aspen Dynamics of the middle vessel batch distillation for the separation of mixtures of ethanol/propanol/butanol. Two configurations of middle vessel batch distillation have been considered, namely, the conventional middle vessel batch distillation (Configuration 1) and the modified middle vessel batch distillation column (Configuration 2). Steady‐state simulations have been performed in Aspen Plus and exported to Aspen Dynamics for dynamic simulation. Dynamic studies show that Configuration 1 requires less time than Configuration 2 to obtain more than 95% of the compositions of ethanol, propanol, and butanol. The efficacy of the two controllers is assessed by the performance indices of integral of square error, integral of absolute error, and integral of time‐weighted absolute error. Configuration 1 is found to have better performance than Configuration 2.

A hybrid batch distillation/membrane process for high purification part 1: Energy efficiency and separation performance study for light impurities removal

High purification processes are usually characterized by high energy demand and unavoidable losses of a purified substance during removal of trace impurities. An unsteady-state hybrid separation method based on a batch distillation with integrated membrane gas separation was studied for high purification of liquefied gases. The performance of a hybrid process versus a standalone batch distillation was analyzed through simulations and experiments for the case of light impurities removal from ammonia. A model of a middle-vessel batch distillation column was built in Aspen Plus Dynamics™ with an integrated hollow fiber membrane model implemented in Aspen Custom Modeler™. The results of batch distillation simulations are validated against the experimental data. Among the considered aspects are the hydrodynamics study, the effect of operating conditions on column separation performance, and the dynamics of the purification process. The simulations were done at a varied impurity cut withdrawal rate, membrane area, stage cut, and membrane selectivity taking into account the effective (mixed gases) selectivity data for ammonia/impurity systems available in the open literature. The possibility of both reducing the total energy input and improving the product recovery is shown for a hybrid purification process involving the separation of the withdrawn impurity cut in a membrane module with recycling of the purified component back to the distillation column.

High-purity liquefied gases: Aspen Dynamics simulation of a purification process in a middle-vessel batch distillation column

The paper explores the use of Aspen Plus and Aspen Dynamics for simulating and optimising a high-precision process of liquefied gases high purification in a middle-vessel packed distillation column. The example studied involves the removal of lower- and higher- boiling impurities from the upper- and lower rectifying sections and maintaining the purified product in the middle vessel. Total reflux operation is studied in the pressure range between the normal boiling point of the purified product and the critical point. Among the considered aspects are the column design and sizing, hydrodynamics study (flooding calculations), the effect of operating pressure and temperature on the thermodynamics of vapour-liquid equilibrium and mass-transfer kinetics in a wide range of operating conditions. The paper demonstrates that the effects and dependencies observed previously through the experiments and by using user-developed custom models are adequately reproduced in the commercial simulator (Aspen Plus) by setting up a fictitious steady-state continuous process with rigorous built-in models. The optimised flowsheet can be converted to Aspen Dynamics as a pressure-driven process where a rigorous dynamic simulation gives a realistic dynamic response, and alternative control structures can be explored.

OPERATIONAL DESIGN AND IMPROVEMENT OF CONVENTIONAL BATCH DISTILLATION AND MIDDLE-VESSEL BATCH DISTILLATION

Abstract 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.

Design and control of a middle-vessel batch distillation for separating DMC–EMC–DEC mixture

Abstract In this paper, the mixture of dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate was separated by middle-vessel batch distillation with feeding in middle-vessel and process control characteristics were researched. The steady state simulation results in Aspen Plus were exported to Aspen Dynamics. Then control effect of liquid level control with HighSelector, composition control (structure1, structure2) and temperature control (proportional action, proportional integration action) were proposed. Composition control structure 2 and temperature control with PI action were investigated to achieve a good control effect.

An energy efficient middle vessel batch distillation: Techno-economic feasibility, dynamics and control

This work aims at developing a novel middle vessel batch distillation (MVBD) through thermal integration route. At first, an internally heat integrated distillation column (HIDiC) configuration is devised for techno-economic feasibility. Under this scheme, the MVBD is divided into rectifying and stripping sections, which are proposed to act as heat source and heat sink, respectively. Utilizing the internal heat source, the utility consumption gets lowered in both reboiler and condenser. Aiming to further improve the energetic potential of this HIDiC configuration of the MVBD column, the vapor recompression (VRC) mechanism is introduced, yielding a hybrid HIDiC-VRC scheme. For a meaningful comparison between all these MVBD column configurations, one needs to operate them at the close, if not same, dynamical response. For this, an open-loop control policy is developed to ensure the optimal use of internal heat source in both the HIDiC and VRC schemes. The proposed HIDiC and HIDiC-VRC structures are evaluated by estimating their respective energy savings of 43.25 and 83.5%, and total annual cost (TAC) savings of 1.17 and 29.17% with reference to a conventional MVBD column. Finally, a comparison of these HIDiC-based schemes is made with the VRC-only of the MVBD.

Design and Control of a Middle Vessel Batch Distillation Process for Separating the Methyl Formate/Methanol/Water Ternary System

The middle vessel batch distillation process for separating the methyl formate/methanol/water ternary system was simulated using Aspen Plus and Aspen Plus Dynamics. The composition control structure (CCS) and temperature control structure (TCS) were studied in a dynamic simulation based on the results of a steady-state simulation. Two temperature control structures, one the traditional TCS and the other TCS with high selectors, show better control performances than CCS. The two control structures can stably control the product purities and liquid holdups in the product vessels at the end of the batch. The results show that TCS with high selectors is better than traditional TCS in terms of the liquid holdups. The performance of the TCS with high selectors is assessed, and controllability is demonstrated.

Aspen Dynamics simulation of a middle-vessel batch distillation process

Aspen Dynamics is a powerful dynamic simulator that is widely used to explore the dynamics and control of continuous processes around some steady-state design operating point. This paper explores its use to study the dynamics of a batch process. The example studied is a middle-vessel batch distillation system for separating a ternary mixture. The batch system is operated by adjusting the two reflux flowrates (one from the reflux drum to the top of the upper column and the second from the middle vessel to the top of the lower column). The liquid inventories in the three drums vary with time. This paper shows how this batch operation can be conveniently simulated by first using the steady-state simulator Aspen Plus to correctly size the equipment. Then the file is exported into Aspen Dynamics where a rigorous dynamic simulation can explore alternative control strategies by using the large library of control functions.

Economic feasibility of a novel energy efficient middle vessel batch distillation to reduce energy use

It has long been recognized that the highly irreversible operation of batch distillation involves more wastage of energy compared to continuous flow distillation. For boosting its energy efficiency, the middle vessel batch distillation (MVBD) column has been invented. In this paper, a rigorous model for an MVBD process for the separation of a ternary hydrocarbon system is developed to simulate its transient behavior. In order to obtain the products at their maximum achievable purities, we device the two operating policies for the representative configuration.This contribution introduces a heat pumping system in the MVBD aiming to further improve its energetic and economic potentials. This novel heat integration technique is operated with a variable speed compressor for pressurizing the overhead vapor before thermally coupling it with the reboiler liquid. Interestingly, along with the compression ratio (CR), the other two manipulated variables are the inflow rate of overhead vapor to the compressor and that of an external medium (here, steam) that provides makeup heat to the reboiler. The operation of this adaptive heat pump assisted column originally involves the simultaneous adaptation of two variables throughout the entire batch processing. The simulation results show that a cost savings predicted in the heat integrated MVBD scheme can be achieved along with a substantial reduction in energy consumption.

Modeling, Simulation and Control of Middle Vessel Batch Distillation Column

Batch distillation is a very efficient unit operation which allows the fractionation of a multicomponent mixture into its pure constituents in a single column. Due to its flexibility and low capital costs, batch distillation is becoming increasingly important in the fine chemicals and pharmaceutical industries. However, the regular batch distillation processes have some disadvantages, such as high energy demands and high temperatures in the feed vessel. An alternative to the regular batch distillation is the middle vessel batch distillation. With this type of process it is possible to obtain simultaneously light and heavy boiling fractions from the top and the bottom of the column respectively and intermediate boiling fraction accumulates in the middle vessel. This work dealing with the modeling and simulation of middle vessel batch distillation column (MVBDC) neglecting the vapor hold and its influence on the process. Modeling of MVBDC is done based on the combined first principle model and empirical relations. The startup of MVBDC is covered. Here we also deal with the control of distillate composition and condenser hold up and process gain estimation. Predominantly theoretical studies regarding controlled variables are studied.

Batch Distillation in a Column with a Side Withdrawal for Separation of a Ternary Mixture with a Decomposing Reaction

The separation of a ternary mixture with a decomposing reaction was investigated in a batch distillation column with a side withdrawal (BDS). The process was simulated by a constant molar holdup model solved by the GEAR integration method and optimized by a simulated annealing algorithm. Comparing to the batch rectifier and middle vessel batch distillation column, BDS is favorable for the purification of an intermediate component from light and heavy impurities with a decomposing reaction. The effects of top reflux ratio and side reflux ratio were also investigated. Different combinations of top and side reflux ratio result in different types of product withdrawal, and the optimal operation tends to be in a large top reflux ratio and a small side reflux ratio.

An evolutionary approach for multi-objective dynamic optimization applied to middle vessel batch distillation

In this paper, a new approach is presented to perform multi-objective dynamic optimizations of novel batch distillation utilizing an evolutionary algorithm. The contribution is divided into two major parts. First, the development of an efficient hybrid evolutionary algorithm covering multi-objective mixed integer dynamic optimization problems is presented. The efficiency of the optimization solver is proven by several complex test problems. Second, the application of the algorithm is shown by the optimization of a middle vessel batch distillation. The challenging non-linear dynamic model, which takes the start-up phase into account, is solved in Aspen Custom Modeler. It could be proven that the proposed evolutionary algorithm can be applied to complex mathematical problems. Likewise the algorithm was found to successfully handle the optimization of middle a vessel batch distillation. The results show the feasibility of the proposed methodology and a significant increase in profitability of the process.

Startup Operation of Middle-Vessel Batch Distillation Column: Modeling and Simulation

The objective of this article is to extensively analyze and discuss the startup of a middle-vessel batch distillation (MVBD) column by means of dynamic modeling and simulation. A rigorous model describing the entire process of an MVBD column including startup from ambient conditions is presented. The model considers the heating of the distillation column and peripheral equipment, as well as the formation and propagation of hydrodynamic and thermodynamic profiles. The physical validity is shown by comparison of simulation studies with experimental results. Sensitivity analyses are used to study startup operation and promote a deeper understanding of the process. General guidelines are provided to standardize and improve the process. The theoretical examinations offer the basis for the development of improved process control strategies and recipe-based automation concepts, as well as for dynamic optimization studies.

Theoretical analysis and operating behaviour of a middle vessel batch distillation with cyclic operation

The present work deals with the cyclic operation of a middle vessel batch distillation (CMVBD). To provide an insight into this highly interesting distillation configuration, theoretical and experimental investigations have been carried out. After a theoretical system analysis, a process control strategy of industrial relevance is proposed. In the experimental part of this work, relevant tasks regarding the dynamic and steady-state behaviour have been considered. This includes the investigation of maximum product qualities and yields as well as the transient behaviour in response to setpoint changes and disturbances. Additionally, a mathematical model of a CMVBD is presented to describe the operating behaviour.

Composition Estimations in a Middle-Vessel Batch Distillation Column Using Artificial Neural Networks

A virtual sensor that estimates product compositions in a middle-vessel batch distillation column has been developed. The sensor is based on a recurrent artificial neural network, and uses information available from secondary measurements (such as temperatures and flow rates). The criteria adopted for selecting the most suitable training data set and the benefits deriving from pre-processing these data by means of principal component analysis are demonstrated by simulation. The effects of sensor location, model initialization, and noisy temperature measurements on the performance of the soft sensor are also investigated. It is shown that the estimated compositions are in good agreement with the actual values.

Dual Composition Control in a Middle-Vessel Batch Distillation Column

The dual composition control problem in a middle-vessel batch distillation column is studied in this work. The control objective is to regulate the overhead purity by manipulating the reflux flow rate and the bottoms product composition by manipulating the boilup flow rate. By using estimators of the input−output modeling error, output-feedback compensators are designed that are shown to be equivalent to a PID controller with an antireset windup structure for the overhead purity regulator and a PI controller with an antireset windup structure for the bottoms composition regulator. Tuning issues are discussed, showing that they have straightforward physical meanings. The ability of the controllers to regulate the overhead product composition and the bottoms product composition in the face of unknown nonlinearities and sampled/delayed measurements is shown via numerical simulations on a dynamical model.