Batch Rectifier Research Articles

Novel use of dividing wall columns for intensification multicomponent batch distillations

While the dividing wall columns for continuous distillations have become quite popular, we present the first detailed analysis of a dividing wall column for batch distillation. For a dividing wall side stripper batch distillation column, we present an operating sequence and its associated mathematical model. Since there are many operating parameter combinations possible for this column, selecting the right operating parameters according to product specifications is presented as an optimization problem. This new configuration's performance is compared with the conventional batch rectifier and the middle vessel columns using two case studies related to the separation of a ternary mixture. The new batch dividing wall column performance is significantly better than the rectifier or the middle vessel column. As the purity specifications increase, the percentage improvement in profit due to the batch dividing wall column compared to the rectifier and the middle vessel columns increases.

Design and comprehensive analysis of a novel pressure-swing batch distillation process for the separation of a binary azeotrope with various boiling behaviors

Batch distillation is widely employed in the fine chemical industry because of its operational flexibility. The mixture of n-heptane and isobutanol exhibits a special azeotropic phenomenon by which it changes from a minimum-boiling azeotrope to a maximum-boiling one with increasing pressure. However, the traditional double column batch rectifier and double column batch stripper processes cannot separate the mixture efficiently. Therefore, the double-column batch stripper–rectifier (DCBS-R) process was designed to obtain high-purity products, based on the azeotropic phenomenon. Further, control structures are explored to achieve stability, and the final purities of the separated products are over 99.9%. Each batch of raw materials is 100 kmol, and the expected annual production capacity is 800 batches. Additionally, a precooler of the low-pressure column (LPC) is introduced to reduce the exergy destruction by exergy analysis. The equipment cost and CO2 emissions are analyzed afterward to optimize the process, based on the multi-objective optimization method. Further, the number of stages and the pressure of the columns are optimized. The optimal obtained total annual cost (TAC) and CO2 emissions of the DCBS-R process are 2.26 × 105 $/y and 4.92 × 105 kg/y, respectively. The partial heat integration is studied to further improve the process performance, thus obtaining TAC and CO2 emissions of 2.22 × 105 $/y and 3.80 × 105 kg/y, which are 7.1% and 22.76% lower than the values obtained from the optimal process, respectively.

Conceptual model-based design and environmental evaluation of waste solvent technologies: Application to the separation of the mixture acetone-water

ABSTRACTIn this paper, two waste solvent technologies are presented as alternatives to the disposal of spent acetone-water mixtures.In the first alternative, a batch rectifier is used to concentrate the waste in order to obtain a distillate with a higher calorific value, which is then sent to off-site incineration either in a cement kiln or in a conventional waste solvent incinerator. The second alternative is a hybrid process composed by a batch rectifier and a pervaporation unit that processes in batchwise mode the first cut from the distillation task to obtain a dehydrated solvent. Here, four scenarios are considered, comprising two kinds of membrane materials and two different vacuum systems.For each alternative, the conceptual design was carried out with the aid of conceptual models of the unit operations involved. Quasi-optimal values for design and operation variables were used as input data to perform an economical and an environmental assessment of each alternative. The economic analysis suggests that the hybrid process is the best alternative given that the replacement cost of fresh solvent (about 850 U$S/ton) is considered as a credit value.From the environmental analysis with life cycle assessment, two main conclusions can be drawn: i) the use of the distillate as an alternative fuel in a cement kiln leads to a reduction in emissions that is relevant for the categories related to human health and ecosystem quality; and ii) in terms of resource depletion, the hybrid process distillation/pervaporation with the ceramic membrane HybSi (Pervatech) shows the lowest impact due to the solvent recovery.

A thermally coupled dividing tower batch rectifier: Energy consumption and cost

In this contribution, a thermally coupled dividing tower batch rectifier (TCDTBR) is proposed. Aiming to boost the fuel efficiency and economic performance, the cylindrical shell of the batch column is horizontally divided into two diabatic sections. A compressor is installed in such a way that one section operates at sufficiently higher pressure than the other one to create a positive thermal driving force between them for feasible heat exchange. The internal heat integration between these two coupled sections in TCDTBR arrangement can be accomplished by using the sequential heat exchangers in the trays. Proposing a variable manipulation policy, this thermal intensification mechanism is demonstrated by a batch rectifier that separates a binary mixture of wide boiling constituents, showing a substantial improvement in both fuel consumption (i.e., energy) and cost savings. Finally, the proposed TCDTBR has shown its superiority over an existing heat integrated batch rectifier with a jacketed reboiler (HIBRJR) on the same example system.

Bottom flashing with interreboiling action in a transient batch rectifier: Economic feasibility, dynamics and control

Abstract This work aims at proposing a batch rectifier with bottom flashing (BRBF) scheme, in which, a fraction of reboiler content is dynamically flashed to lower its temperature so that the exiting liquid can be used as a heat sink against the overhead vapor (heat source) in the condenser. Receiving latent heat from that vapor, the flashed liquid gets vaporized and merges with the flashed vapor. Recovering pressure of this combined stream, it is used as a boil-up vapor in the reboiler, thus lowers the external heat duty. By this way, the proposed BRBF arrangement reduces the utility consumption in both the reboiler and condenser. To improve the energetic potential further, the boil-up vapor produced in the flashing loop is proposed to split into a couple of fractions and distributed in intermediate stage(s) along with the reboiler. The BRBF coupled with this interreboiling action is subjected to economic feasibility test, for which, the concerned column configurations need to be dynamically close, if not same. Since the batch processing is inherently a transient operation, it is not trivial to have their dynamics close. To make the comparison meaningful, we formulate an open-loop control scheme that makes sure that the BRBF follows the conventional batch rectifier (CBR) dynamics, which is used as a basis. Finally, a binary system is simulated to demonstrate the proposed BRBF with and without interreboiling. It is investigated that the BRBF configuration provides an about 68% energy savings with a payback time of 3 yr. Further, proposing interreboiling in the BRBF column increases the energy savings to 81%, reducing the payback time to 2.32 yr.

Comparison of Closed and Open Operation Modes of Batch Distillation

Open and non-conventional closed batch column operation modes were compared by rigorous simulation. The configurations studied were the batch rectifier (“two vessel column”), middleand multi-vessel column (“three and four vessel columns”). For the operation in closed system we studied six different modes differing in the operation of the vessels. We simulated the separation of test mixtures (n-hexane(A)-n-heptane(B), AB-n-octane(C), A-B-C-n-decane(D)), and compared the recoveries under constant product purities. The effects of the operational parameters were also studied.

An energy‐efficient cost‐effective transient batch rectifier with bottom flashing: Process dynamics and control

Exploring an internal heat source through bottom flashing route, this work introduces a dynamic batch column configuration within the framework of mechanical heat pump system. This batch rectifier with bottom flashing (BRBF) scheme attempts to use the reboiler liquid as a heat exchanging medium in the overhead condenser, thereby avoiding the use of any external coolant stream and reducing the consumption of hot utility in the reboiler. Aiming to operate the proposed transient process unit at an optimal state of energy use, we formulate an online open‐loop control policy that estimates the multiple control actions simultaneously. Furthermore, in order to achieve constant product purity, a gain‐scheduled closed‐loop control system is synthesized with keeping the stability margin constant. Simulating a multicomponent reactive system, the novel BRBF arrangement is evaluated in the aspects of energy savings and cost under both the open‐loop and closed‐loop control modes. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3699–3707, 2015

A novel combination of internal and external heat integrations in batch distillation: Application to a reactive system

Studies on the thermal integration of batch rectifier have received almost no attention, although it is well-known for continuous distillation since the 1960s. In this contribution, we aim to develop an energy integration approach for batch distillation columns by thermally coupling the rectification tower with the concentric reboiler that surrounds the tower as a jackted. In this internally heat integrated batch distillation with a jacketed reboiler (IHIBDJR), the vapor produced in the concentric reboiler is compressed and then it enters the bottom of the rectifier. With the judicious use of internal heat source, the proposed IHIBDJR shows its attractiveness in terms of energy savings and payback time of excess capital. The pressure elevation from the jacketed reboiler to rectifying section generates a possibility of further intensification through the introduction of direct vapor recompression mechanism in the IHIBDJR. This novel combination of internal and external heat integrations can utilize the latent heat, an additional internal source, released by the compressed overhead vapor in vaporizing the reboiler liquid. After deriving the general form of this combined heat integrated structure, the mechanism is finally illustrated by a batch reactive distillation. This hybrid configuration shows promising energetic and economic potential over the IHIBDJR and its conventional counterpart.

Incorporating Pinch Distillation Boundaries into the Conceptual Modeling of Batch Distillations: Ternary Mixtures

This contribution explores the influence of curved unstable distillation boundaries on the performance of batch distillations in ternary mixtures and its incorporation into a conceptual modeling framework under the assumption of a batch rectifier with an infinite number of stages. First, the concept of preferred separation in batch distillation is presented. Calculation of “pitchfork” distillation boundaries is then determined using a robust predictor-corrector algorithm based on improved memory method with the purpose of estimating the maximum feasible distillate composition in the preferred separation line. Four highly nonideal systems are studied. Finally, the model is extended to allow simulation of the operation at different reflux policies. Results of a complete simulation performed with the enhanced conceptual model are shown for the system octane/2-ethoxyethanol/ethylbenzene.

Comparative control study of a simulated batch rectifier

This article proposes a nonlinear control strategy for a batch rectifier. The hybrid control strategy comprises a state estimator, namely Luenberger-like nonlinear estimator (LNE) and the feedback linearizing controller (FLC). The observation scheme aims to estimate the imprecisely known parameter based on the available measurement. For the representative distillation unit, the state predictor is formulated using only a component material balance equation around the condenser–reflux drum system. It clearly indicates the existence of a process/model mismatch and this discrepancy is efficiently taken care of by the corrector part of the LNE. In the subsequent phase, the FLC is synthesized for the example system. The derived nonlinear FLC–LNE controller shows better performance compared to a traditional proportional integral (PI) law. The simple structure, straightforward design and good performance make this nonlinear controller attractive for online use.

Separation of a Chloroform–Acetone–Toluene Mixture by Pressure-Swing Batch Distillation in Different Column Configurations

In this paper, a new, triple-column configuration application is introduced to separate ternary mixtures by pressure-swing batch distillation. This study investigates the separation of a chloroform–acetone–toluene ternary mixture in different column configurations (a combination of the batch stripper and the double-column batch rectifier, the double-column batch rectifier, and the triple-column configuration) by a feasibility study and by rigorous simulation and compares these processes at two different charge compositions by its overall specific energy consumption. The influences of the most important operational parameters are studied for all processes, and the performances of the column configurations are compared. On the basis of the results, we state that the triple-column configuration is more efficient than the other column configurations investigated.

Batch Distillation in a Batch Stripper with a Side Withdrawal for Purification of Heat-Unstable Compounds

Batch distillation in a batch stripper with a side withdrawal (BSS) for the purification of heat-unstable compounds from light and heavy impurities was investigated. The batch distillation process was simulated by a dimensionless dynamic model and optimized by simulated annealing algorithm. Batch distillation in a BSS was compared with that in a batch stripper (BS) for the purification of heat-unstable compounds with different types of degradation reactions. The recovery of heat-unstable compounds in a BSS is larger than that in a BS, especially in the case of the heat-unstable compound converting to a heavy impurity. Compared with batch distillation in a batch rectifier with a side withdrawal (BRS), batch distillation in a BSS is more suitable for purification of heat-unstable compounds that convert to a light impurity. The effects of operational and design parameters for batch distillation in a BSS were discussed according to the simulation results, such as the temperature in the top storage vessel, the location of the side withdrawal stage, the holdup in the reboiler, the reboiler ratio, and the side reflux ratio.

Pressure swing batch distillation by double column systems in closed mode

Two new double column systems operated in closed mode are suggested for pressure swing batch distillation. These configurations are investigated by feasibility studies based on several simplifying assumptions (e.g., infinite plate number, no stage hold-up) and are compared with double column batch rectifier and double column batch stripper in open mode. We study the configurations also by rigorous simulation based on less simplifying assumptions using a professional dynamic simulator. For the different configurations the influence of the most important operational parameters is studied. The results obtained for open and close modes are compared. The calculations and the simulations are performed for a binary minimum (acetone–n-pentane) and for a maximum (ethylene-diamine–water) azeotrope mixture.

The energy consumption in a batch stripper and a batch rectifier

The energy consumption in a batch rectifier and a batch stripper was investigated with a shortcut mathematical model. The minimum energy consumption of a batch stripper was compared to that of a batch rectifier under “general constant reflux” and “general constant distillate composition” with the ratio of minimum energy consumption E S /E R . When the feed contains a large amount of light component, the product purity specification is low and the relative volatility is small, the minimum energy consumption of a batch stripper is less than that of a batch rectifier under “general constant reflux” and “general constant distillate composition”. When the feed contains a small amount of light component, the product purity specification is very high and the relative volatility is low, a batch stripper can also consume less energy only in the “general constant distillate composition” operation mode. In other cases, a batch rectifier can consume less energy.

Process Simulation and Design of Reactive Distillation Column

This paper presents a systematic study on the homogeneously catalyzed reactive distillation (RD) process operated in both batch and continuous mode for the synthesis of ethyl acetate. In the first part, the fundamental model has been developed incorporating the reaction term within the model structure of the nonreactive distillation process. In case of batch rectifier, the process operation is simulated at the startup phase under total reflux condition for reaching the steady state. The open-loop process dynamics are also examined running the batch process at production phase under partial reflux condition.The concerned batch rectifier has the ability to provide high purity product. On the other hand, the continuous RD column exampled at the beginning of the second part produces relatively low quality product. In the present study, an attempt has been made to configure a feasible continuous column with improved product quality. In order to propose a RD setup, several simulation experiments have been performed for sensitivity analysis. An interesting phenomenon, the input multiplicity, is observed for both the batch as well as continuous column.

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.

Thermodynamic Insights on the Feasibility of Homogeneous Batch Extractive Distillation, 2. Low-Relative-Volatility Binary Mixtures with a Heavy Entrainer

All former studies reported that the separation of the low relative volatility binary mixture by using a heavy entrainer in a batch rectifier imposed the obligatory withdrawal of the most volatile original component. In this paper, we demonstrate that this does not always happen and that the product sequence can be unambiguously determined from the sole analysis of thermodynamic properties of residue curve maps and the occurrence of unidistribution lines and univolatility lines, following the general feasibility criterion enounced in part I for the separation of azeotropic mixtures using heavy or light entrainers. For low relative volatility mixtures, the original component having an intermediate boiling temperature can be also drawn as the first distillate product. Cases concerning 94% of statistically occuring zeotropic ternary mixtures are investigated, allowing to define the product sequence without any previous calculation of the liquid composition profile inside the column. Preliminary feasibility results are confirmed by computing maps of extractive and rectifying liquid composition profiles using a simplified mass balance. Final validation is done via rigourous simulation using ProSim Batch software.

New double column system for heteroazeotropic batch distillation

A new double column system (DCS) operated in closed mode is suggested for heterogeneous batch distillation. This configuration is investigated by feasibility studies based on the assumption of maximal separation and is compared with the traditional batch rectifier (BR). We study the configurations also by dynamic simulation based on a detailed model using a professional simulator. For the new configuration the minimal duration of the process is determined. The influence of the most important operational parameters is studied. The calculations and the simulations are performed for a binary (n-butanol–water) and for a ternary heteroazeotropic mixture (isopropanol–water + benzene as entrainer). One of the advantages of the DCS is that distillation of binary and ternary systems is performed in only one step. Furthermore the recovery of components is usually higher and the amount of byproducts is lower.

Feasibility of new pressure swing batch distillation methods

The pressure swing distillation in different batch column configurations is investigated by feasibility study and rigorous simulation calculations. Besides studying the well known batch configurations (rectifier, stripper, middle vessel column) we also suggest two novel configurations such as double column batch rectifier (DCBR) and double column batch stripper (DCBS). The alternate application of a batch rectifier and a batch stripper is also studied. The feasibility method is based on the assumption of maximal separation. The results of the feasibility studies are verified by rigorous simulations based on less simplifying assumptions. The calculations are made by a professional dynamic flow-sheet simulator for the separation of a minimum (ethanol–toluene) and a maximum boiling (water–ethylene-diamine) azeotropic mixture. The different column configurations are compared. The DCBS (for the separation of the minimum azeotrope) and the DCBR (for the maximum azeotrope) showed several advantages (e.g. only one production step without pressure change, lower energy consumption) compared with the other configurations.

NEW COLUMN CONFIGURATIONS FOR PRESSURE SWING BATCH DISTILLATION II. RIGOROUS SIMULATION CALCULATIONS

The pressure swing distillation in different batch column configurations is investigated by rigorous simulation calculations. The calculations are made by a professional flow-sheet simulator for the separation of a minimum (ethanol-toluene) and a maximum boiling (water- ethylene-diamine) azeotropic mixture. Besides studying the well known configurations (rectifier, stripper) we also investigate two novel configurations such as double column batch rectifier and double column batch stripper. The alternate application of a batch rectifier and a batch stripper is also studied. The different column configurations are compared.