Vapor Recompression Column Research Articles

Enviro-economic investigation of Novel heat-integrated configurations for pressure swing distillation

Pressure Swing Distillation is a widely adopted solution for the separation of pressure-sensitive azeotropic mixtures in various chemical industries. While this method yields high-purity products, it comes with inherent challenges such as elevated operating costs and energy consumption. However, the temperature differential between the two columns involved presents a compelling opportunity for heat integration. In this study, 18 distinct heat integration scenarios were systematically evaluated using a process simulation software to identify the optimal column configuration for minimizing the Total Annualized Cost. These scenarios span five categories: the Conventional Method, Partial Heat Integration, Full Heat Integration, Internal Heat Integration Distillation Column, and External Heat Integration Distillation Column. The Vapor Recompression Column and Divided Wall Column schemes were applied to each method. Genetic Algorithm served as the optimization tool to determine the best arrangement with TAC as the objective function. Additionally, the environmental impact, assessed through CO2 emissions, was considered. Results indicate that the most economically and environmentally friendly solution is the I-HIDiC with divided wall columns, incorporating VRC systems in both columns. This approach offers a remarkable 66.5% cost savings and a substantial 96.3% reduction in CO2 emissions.

Propán-propilén elegy elválasztásának vizsgálata VRC rendszerrel

In this study a propane-propylene separation is investigated with traditional distillation column and with vapor recompression column (VRC). It is a very energy-intensive process, mainly because the boiling points of the components differ only slightly. The systems with the same parameters of the feed are investigated with Unisim Design® process simulation software with SRK equation of state. The results show that in case of the traditional and VRC system the quality and quantity of the products are the similar, but the energy stream of the VRC system is much lower than the traditional column’s. During the study not only the energy consumption but also the costs of the utility streams are calculated. The traditional distillation column includes a reboiler and a condenser, while the VRC system has energy streams from a compressor and a condenser. The calculation results show that the cost of the utility streams used in the VRC system is 15.5% of the costs of the utility streams in the conventional system.

Thermodynamic evaluation of the novel distillation column of the air separation unit with integration of liquefied natural gas (LNG) regasification

A cryogenic air separation unit (ASU) with the implementation of vapor recompression column (VRC) and LNG cryogenic energy is proposed and investigated. To this end, three types of cryogenic rectification column for air separation are first illustrated, and their thermodynamic characteristics are evaluated by the first and second thermodynamic laws. The results show the purity and recovery ratio of product are determined by the total amount of heat duty and the scheme of heat distribution. Compared with the conventional double rectification column and internally heat-integrated distillation column, the VRC is the most suitable column for the ASU with use of LNG cryogenic energy as its lower demand of shaft work and minimum energy of separation. Based on the above analysis, adopting the cryogenic energy from product to cool the reflux and feed air is beneficial for producing vapor product in the proposed process. The operating pressure of ASU could be reduced by about 24%, and the cryogenic energy of LNG can be used efficiently and sufficiently with respect to the supercritical thermophysical property. By adding the air-aid refrigeration process, the proposed process also has the ability to produce liquid oxygen. Under the same oxygen purity and recovery ratio, the optimal results show the power consumption is about 6.9% and 11.1% lower than that in the previous studies in producing vapor and liquid product respectively, and the minimum energy of separation is improved by use of LNG cryogenic energy.

HIDiC Configuration Selection Based on Exergetic Analysis

The present study shows an exergy-based strategy for defining the type of Heat Integrated Distillation Column HIDiC, most suitable for separating the propylene-propane system. For comparing and validating the results, the analysis was performed on conventional column, vapor recompression column (VRC) and several HIDiC configurations: Top, Bottom, Basic, Optimal and Total. Uniform heat transfer area was used for the heat distribution between the internal and external column sections. As main result, it was found that Top HIDiC has the best performance among the HIDiC configurations with a 66.4% of exergy saving compared to a conventional column, followed by the Total HIDiC with a 43.4%. In fact, Top HIDiC shows better exergetic behavior than VRC (55.0% of exergy saving), which is currently used in the industry for the separation of the studied system. Additionally, results confirm that the selection of the configuration for energy integration is not an obvious task and that the presented strategy can be applied for the analysis of the separation of other mixtures.

Simulation and optimization of different pressure thermally coupled distillation for separating a close-boiling mixture of n-butanol and iso-butanol

Substantial quantities of energy are required in conventional distillation columns applied in high-purity separation of close-boiling mixtures. To achieve energy saving of distillation, a novel different pressure thermally coupled distillation (DPTCD) was proposed for separating the close-boiling mixture of n-butanol and iso-butanol. Both this intensified energy integration technique and two other processes, namely conventional distillation (CD) and vapor recompression column (VRC), were simulated in process simulator Aspen Plus. The optimization was carried out to determine the optimal values of design and operating variables on the basis of minimizing energy consumption. Subsequently, the energy saving and economic efficiency of the DPTCD scheme were evaluated through the comparison with the other two processes. The results showed that, compared to the CD and VRC processes, the energy consumption of DPTCD process was decreased by 65.21 and 15.79%, respectively, and the total annual cost (TAC) of DPTCD process can be reduced by 33.75 and 10.46%. It demonstrated that DPTCD scheme was the most promising alternative to reduce the total energy consumption and TAC with high purity (99.1 wt%) n-butanol and iso-butanol products among these separation processes.

Systematic design of the integrating heat pump into heat integrated distillation column for recovering energy

Many developed energy efficient configurations based on heat-integrated distillation column (HIDiC) have been proved to be attractive separation alternatives for saving energy. The key limitation of heat integrated technology is how to build splendid schemes for the heat integrated distillation column. In this work, the overall economic evaluation of conventional distillation column (CDiC), basic heat-integrated distillation column (basic HIDiC) and vapor recompression column (VRC) were executed systematically. Based on the comparison of results, by coupling the basic HIDiC with heat pump technology, a new distillation process model was developed as an intensified HIDiC (int-HIDiC) configuration for propylene-propane splitter. By this enhanced heat integration, the reboiler and the low pressure steam were no longer needed in the process. Meanwhile, the heat distribution proportion and the corresponding operating conditions of this int-HIDiC were optimized through vast simulations and computations. Finally, based on the above optimization results, we developed a simplified HIDiC configuration with two separated columns. The results show the better economic and energy performances than all the other energy-saving schemes including VRC.

Modeling and analysis of conventional and heat‐integrated distillation columns

A generic model that can cover diabatic and adiabatic distillation column configurations is presented, with the aim of providing a consistent basis for comparison of alternative distillation column technologies. Both a static and a dynamic formulation of the model, together with a model catalogue consisting of the conventional, the heat‐integrated and the mechanical vapor recompression distillation columns are presented. The solution procedure of the model is outlined and illustrated in three case studies. One case study being a benchmark study demonstrating the size of the model and the static properties of two different heat‐integrated distillation column (HIDiC) schemes and the mechanical vapor recompression column. The second case study exemplifies the difference between a HIDiC and a conventional distillation column in the composition profiles within a multicomponent separation, whereas the last case study demonstrates the difference in available dynamic models for the HIDiC and the proposed model. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4251–4263, 2015

A hybrid heat integration scheme for bioethanol separation through pressure-swing distillation route

In this contribution, a hybrid thermal integration scheme is proposed for a pressure-swing distillation (PSD) column by combining an internally heat integrated distillation column (HIDiC) with vapor recompression column (VRC). The purpose of this article is three fold: first, it designs a HIDiC for a PSD system with a reduced number of internal heat exchangers. Second, it develops a hybrid column configuration by integrating that HIDiC, which is devised based on the thermal driving force existed between the two diabatic columns, and VRC that is devised based on the thermal driving force existed between the top and bottom of the same high pressure column, yielding an ideal HIDiC–VRC configuration. Third, it provides a comprehensive comparison between the HIDiC-alone and its hybrid HIDiC–VRC structure with reference to a conventional standalone PSD column. To evaluate the performance of all these configurations, we estimate the two performance indexes, namely energy consumption and total annual cost, for an example of a bioethanol dehydration system.

Economic optimization of heat pump-assisted distillation columns in methanol-water separation

Finding efficient alternative to CDiC (Conventional Distillation Column) for methanol-water separation has been an attractive field of study in literature. In this work, five heat pump-assisted schemes are proposed and compared to each other to find the optimal one; (1) VRC (Vapor Recompression Column), (2) external HIDiC (Heat-Integrated Distillation Column), (3) intensified HIDiC with feed preheater, (4) double compressor intensified HIDiC-1, and (5) double compressor intensified HIDiC-2. GA (Genetic Algorithm) is then implemented for optimization of the schemes when TAC (Total Annual Cost) is its objective function. During optimization, two new variables are added for using only appropriate amount of the overhead stream in VRC and double compressor intensified HIDiCs, and another new binary variable is also used for considering feed preheating. Although TAC of the intensified HIDiC with feed preheater is found higher than CDiC by 25.0%, all optimal VRC, external HIDiC, double compressor intensified HIDiCs schemes are reached lower optimal TAC by 3.1%, 27.2%, 24.4%, and 34.2%. Introduced for the first time, the optimal scheme is the double compressor intensified HIDiC-2 with 34.2% TAC saving, 70.4% TEC (Total Energy Consumption) reduction with payback period of 3.30 years.

Assessing the performance improvement of an intensified heat integration scheme: Reactive pressure-swing distillation

Declining petroleum reserves, increasing fuel demands and environmental problems have attracted increasing research attention in improving the energetic potential of separation processes dominated by distillation. In this contribution, we develop an intensified thermal integration scheme for a pressure-swing distillation (PSD) by combining the internally heat integrated distillation column (HIDiC) and the vapor recompression column (VRC), thereby acquiring the benefit of both of them. Since the PSD process typically combines a low-pressure (LP) and a high-pressure (HP) distillation unit, the possibility of thermal coupling arises between the HP column (heat source) and the LP column (heat sink) within the framework of HIDiC scheme. Aiming to further reduce the consumption of external energy in the PSD system, the overhead vapor of HP column is proposed to act as a heat source for bottom liquid reboiling in the LP column by the application of VRC mechanism. By this way, the HIDiC-VRC combination gets the shape of an intensified structure and it is capable of providing an enhanced energy efficiency potential. For a reactive pressure-swing distillation (reactive PSD), the proposed HIDiC-VRC configuration is shown to be more energy efficient and cost-effective compared to the HIDiC-alone scheme.

Introducing vapor recompression mechanism in heat‐integrated distillation column: Impact of internal energy driven intermediate and bottom reboiler

A novel combination of internally heat‐integrated distillation column (HIDiC) and vapor recompression column (VRC) with intermediate reboiler (IR) is proposed. Supplying heat at the highest temperature point (i.e., column bottom) of the VRC scheme is not thermodynamically favorable and, therefore, we aim to install the IR for better distribution of heat along the column length, thereby reducing the compressor work. Introducing IR in the combined HIDiC‐VRC system formulates an open‐loop variable manipulation policy to evaluate the comparative impact of internal and external heat sources on bottom liquid reboiling. With internal energy driven bottom reboiler, we further investigate the hybrid HIDiC‐VRCIR column with proposing the two modes of compressor arrangement, namely parallel and series. Finally, a multicomponent distillation system is exampled to show the promising potential of the proposed HIDiC‐VRCIR configurations in improving the energetic and economic performance over the HIDiC‐alone and HIDiC‐VRC schemes with reference to a conventional standalone column. © 2014 American Institute of Chemical Engineers AIChE J, 61: 118–131, 2015

Feasibility study of heat-integrated distillation columns using rigorous optimization

In this work, rigorous optimization of HIDiC (Heat-Integrated Distillation Column) and VRC (Vapor Recompression Column) is implemented by GA (Genetic Algorithm) to find an alternative for CDiC (Conventional Distillation Column). The objective function is TAC (Total Annual Cost). Three different case studies are investigated, being composed of benzene-toluene, propane-propylene, and methanol-water. A novel strategy is proposed to consider all the heat integration possibilities resulting in more efficient search space than our previous attempt. It is observed that the heat exchangers arrangement of optimum HIDiCs are very similar to VRCs in ideal case studies. Although CDiC is the optimum configuration in the benzene-toluene separation, 6.6% reduction is achieved for the presented HIDiC compared to previous work. For propane-propylene splitter, VRC is the economical alternative with a 44.1% decrease in the TAC of CDiC. Moreover, VRC and HIDiC optimizations leads to 25.5% and 4.4% reductions in TAC compared to previous work, respectively. However, for the non-ideal methanol-water separation, which has a wide boiling point range, the TAC of optimum HIDiC is surprisingly lower than CDiC and optimum VRC by 3.4% and 31.2%, respectively.

Optimal design of cryogenic distillation columns with side heat pumps for the propylene/propane separation

Propylene is one of the most important products in the petrochemical industry, which is used as raw material for a wide variety of products. The propylene/propane separation is a very energy-intensive process because their boiling points are quite similar. In addition, at atmospheric conditions, their boiling points are −47.6°C and −42.1°C, respectively. To separate this mixture conventional columns which operate at high pressure and cryogenic distillation columns which operate at low pressure have been used, however, this approaches are still energy-intensive. This work presents energy-efficient and intensified distillation columns which are adiabatic such as the vapor recompression column (VRC) or diabatic such as columns with heat-integrated stages. A design and optimization procedure, which minimizes the energy consumption in the propylene/propane separation is presented. Conceptual design, superstructure representation, rigorous simulations and mathematical programming techniques are effectively combined to assess all the candidate distillation structures, refrigeration cycles, and heat integration possibilities simultaneously. Results showed that VRC and diabatic distillation columns with heat-integrated stages can reduce the energy consumption between 58 and 75% when compared with conventional distillation at high pressure. Furthermore, the proposed synthesis procedure derived simplified optimal distillation structures with few heat-integrated stages and still attained important energy savings.

Internal and external HIDiCs (heat-integrated distillation columns) optimization by genetic algorithm

HIDiC (Heat-Integrated Distillation Column) is an effective energy-saving configuration especially for the separation of close boiling point mixtures. In this work, the stochastic methodology has been applied for optimization of both internal and external HIDiCs. The use of GA (Genetic Algorithm) to find the optimal HIDiC configuration is presented while the fitness function is set to be the TAC (Total Annual Cost). HIDiC simulation has been performed based on the modified MESH equations using a rigorous thermodynamic model. Introducing a novel integer variable (the Layout number) leading to a more effective solution for the examined case study. This variable can generate systematically more energy efficient candidates for both internal and external HIDiCs. Benzene-toluene separation has been investigated by the proposed optimization procedure. The multivariable problem can be successfully optimized by GA while a good initial estimation is not essential. Based on the final results, up to 6.60% and 9.75% TAC reduction have been accomplished in external and internal HIDiCs optimization using the proposed method compared to the reported solutions in a previous work for the examined case study. However, VRC (Vapor Recompression Column) optimization at the end of presented work results 7.89% TAC reduction rather than optimal HIDiC.

Improving energy efficiency and cost-effectiveness of batch distillation for separating wide boiling constituents. II: Internal versus external heat integration

In the first paper of this series, we developed a vapor recompressed batch distillation (VRBD) scheme by means of external heat integration. This contribution aims at devising an internally heat integrated batch distillation with a concentric reboiler (IHIBDCR) configuration, in which the rectifying tower is surrounded by a jacket. The operating cost can be reduced with the improvement of energy savings substantially through seeking further external heat integration under the framework of vapor recompression mechanism in the IHIBDCR structure between the overhead vapor and the reboiling liquid. The features of both the IHIBDCR system and its hybrid form that combines the vapor recompression column (VRC) and the IHIBDCR scheme are illustrated by a binary mixture having wide boiling constituents, with special emphasis focused on the comparative performance study between the externally integrated VRBD presented in Part 1 of the current work, the internally integrated IHIBDCR arrangement and the hybrid structure.

Assessment of the implementation of vapor recompression technique in batch distillation

As the cost of energy continues to rise and the alarm bell on global warming has started ringing, it becomes imperative to reduce energy consumption by improving the thermodynamic efficiency of industrial processes. In this light, the direct vapor recompression column (VRC) has emerged as an attractive scheme by means of thermal intensification with great potential for energy saving. Although the external heat integration through VRC route has been proved to be an effective way for the enhancement of thermal efficiency of continuous distillation columns, the research on vapor recompressed batch distillation (VRBD) has just started. In this novel thermally integrated VRBD system, either the vapor inflow rate to the compressor or the external heat input to the reboiler is manipulated throughout the unsteady state batch operation. In order to broaden its applications, in this contribution, we aim at exploring the energetic and economic potentials of VRBD structure for the separation of a nonreactive binary system in addition to a complex reactive multicomponent mixture. Simulation results show the superiority of the VRBD column over the conventional standalone column in both the cases.

Improving Energy Efficiency and Cost-Effectiveness of Batch Distillation for Separating Wide Boiling Constituents. 1. Vapor Recompression Column

Although the direct vapor recompression column (VRC) has been known for its application in continuous distillation since the 1960s, the research on vapor recompressed batch distillation (VRBD) started a couple of years ago. In this contribution, a batch splitter assisted by a heat pump of the vapor recompression type is investigated by rigorous method. When the VRC system is employed in batch processing, a variable manipulation procedure has to be adopted, leading to the adjustment of either the vapor inflow rate to the compressor by splitting the overhead vapor or the external heat input to the reboiler. The present work aims at exploring the operational and economical feasibility of the VRBD column for the fractionation of a mixture consisting of wide boiling components. By separating this binary mixture, it is quantitatively shown how closely the reversible batch operation can be approximated by using the direct compression of overhead vapor. To further strengthen the advantages of the VRC scheme over its conventional counterpart, a variable speed VRBD structure is proposed by introducing a variable speed compressor in the VRBD configuration aiming to run the column at a controlled compression ratio.

A novel multistage vapor recompression reactive distillation system with intermediate reboilers

Most of the published studies have focused on the thermal integration of nonreactive distillation columns. The key limitation of reactive distillation (RD) technology is that the necessary conditions (such as pressure and temperature) for the reaction must match those of distillation. Owing to this constraint, the reaction conversion may be adversely affected at the elevated pressure in the reactive section of an internally heat integrated distillation column (HIDiC). This fact forces us to adopt an external heat integration approach for an industrial heterogeneously catalyzed ethyl tert‐butyl ether (ETBE) RD column. The direct vapor recompression column (VRC) is an external heat integration scheme that is successfully used as an energy efficient scheme for separating a close‐boiling mixture. Interestingly, there exists a large temperature difference between the two ends of the representative ETBE column, and it makes the external heat integration more challenging. Aiming to improve the thermal efficiency of the ETBE column under the VRC framework, various heat pump arrangements with intermediate reboiler(s) (IR(s)) are explored and analyzed with performing a comparative study in terms of energy consumption and economics. To improve further the thermal efficiency, in this contribution, a novel multistage vapor recompression RD column with IRs is introduced addressing a number of practical concerns. An algorithm for the proposed column is formulated showing the sequential steps involved in heat integration. It is inspected that the proposed multistage vapor recompression RD system appears overwhelmingly superior to the classical vapor recompression RD and its conventional stand alone column providing a significant savings in energy as well as cost. © 2012 American Institute of Chemical Engineers AIChE J, 59: 761–771, 2013

A novel intensified heat integration in multicomponent distillation

In this contribution, a novel intensified heat integrated ternary distillation column (int-HITDiC) is introduced. The objective is to show the superiority of the int-HITDiC over its general form, namely the HITDiC and the conventional standalone column on the basis of two criteria: energy consumption and economics. The concept of pinch technology has been applied to identify the feasibility region for internal thermal coupling between two diabatic sections, namely the rectifying section and stripping section. In this study, the influence of system parameters on the behavior of HITDiC is examined. The optimum compression ratio is arrived at by taking into account the energetic and economic aspects. Performing a detailed analysis, it is observed that the general HITDiC scheme shows lower energy consumption and better economic figure compared to its conventional counterpart. Aiming to improve the overall efficiency further, the int-HITDiC scheme has been explored. The proposed intensified strategy gets the advantage of both HIDiC and direct vapor recompression column (VRC).

Comparison of Energy Usage for the Vacuum Separation of Acetic Acid/Acetic Anhydride Using an Internally Heat Integrated Distillation Column (HIDiC)

Energy savings for an internally heat-integrated distillation column (HIDiC) and a vapor recompression column for the vacuum separation of acetic acid/acetic anhydride was theoretically analyzed and compared to the simulation of a reference column configuration of the Eastman Chemical Company using ASPEN Plus. In these simulations, the design and operating variables were defined and optimized to minimize total energy used. The effects of design variables such as quantity and location of the heat integration stages, reflux ratio, and rectifying section absolute pressure on energy consumption and product purity revealed that one HIDiC configuration had 62% energy savings over the reference column. The distillation column using vapor recompression was evaluated as a benchmark for comparing the HIDiC configurations and the reference column. The VRC column simulation predicted both increased product purity and an energy savings of 91% over the reference unit.