Distillation Column Sequences Research Articles

Automatic Design and Optimization of Column Sequences and Column Stacking Using a Process Simulation Automation Server

Simulation–optimization is applied to determine nearly optimal process designs in column sequencing and stacking problems using a simulated annealing algorithm (SAA) in the client (MATLAB) and a single distillation column in the server (Aspen Plus). Each column in every sequence is optimized separately, and the total cost of each sequence is calculated. This method benefits from both the rigor of column modeling in a process simulator and the flexibility of implementing sequential procedures and derivative-free optimization in a procedural programming language. Using this method, a single column can be optimized within 6 min of computer time. Furthermore, when stacking rules and available utilities are specified, a nearly optimal heat-integrated distillation column sequence can be designed automatically. Results are illustrated using two case studies of column sequencing problems.

Energy Integrated Distillation Column Sequence by Driving Force Method and Pinch Analysis

Distillation is a common separation process since its emergence in the early 20th century due to its capability for mass production without compromising the product(s) quality. However, the energy efficiency is still become the challenge for the industry players. Since then, they put so much effort in ensuring the energy efficiency of the process. It is not only for economic purpose but also to address the environmental issue whereby the legislation become stringent over the years. Therefore, this paper aims to investigate the energy efficiency of distillation column sequence by using the pinch analysis method. Rigorous simulation of the distillation for component n-butane, n-hexane, n-heptane and n-nonane has been carried-out for 5 different sequences namely direct, indirect, driving force sequence (indirect-direct), direct-indirect and split for energy analysis. Aspen HYSYS V9 has been used for the simulation while the data was extracted for pinch analysis including the construction of problem table algorithm to obtain the minimum cooling and heating load for each sequence. The results that were analyzed and compared including total heat load, heating load and cooling load. Then the grid diagrams for the best sequence was constructed. From the results of energy analysis, all distillation sequences except for direct-indirect sequence recorded further energy saving compared to the base case whereby the highest saving is driving force sequence at 6.31% total energy saving. It also recorded the highest percentage of heating and cooling load at 4.85% and 9.05% respectively. This paper also strengthens the advantage of driving force method in determining the best sequence since it was proved to produce lower energy consumption compared to others. Then, the energy can be further reduced by using the pinch analysis. Therefore, for this case study, it can be concluded that the heat integration via pinch analysis is a promising method for further saving for any distillation column sequence.

Energy Integrated Distillation Column Sequence by Driving Force Method and Pinch Analysis for Five Components Distillation

Distillation is an energy-driven process that is recognised as the most widely used in chemical and petrochemical industries. Energy efficiencies have always been the key issue for this technology to survive. Therefore, this paper aims to investigate the use of driving force method to determine the best distillation sequence for energy efficiency. The method is supported using pinch analysis for the opportunity to extend the energy saving in the process. The distillation process involved five alkanes components which are n-hexane, n-heptane, n-octane, n-nonane and n-decane. The rigorous simulations for 14 possible distillation column sequences including driving force sequence have been carried-out by using ASPEN HYSIS V9 software. Then, the data were extracted for pinch analysis and the best sequence was determined based on total load, heating load and cooling load. The grid diagram for heat exchanger network was then proposed for the best sequence. From the results, it can be claimed that the use of pinch technology enhanced the energy saving most of the sequences. The best sequence is sequence no. 9 that recorded percentage saving of 34.83 % for total load, 33.87 % for heating load and 35.84 % for cooling load. On the other hand, driving force sequence (sequence no. 5) also accounted as one of the highest efficiency and still become an attractive method for best sequence determination. As a conclusion, further energy saving can be achieved via the use of pinch analysis in any distillation sequence.

Control properties of driving force based distillation columns design

So far, not much is known about the controllability of distillation columns derived from algorithms as there are many types of algorithms exist and many forms of mixtures to be separated. It is therefore aimed in this study to analyse the controllability of a distillation columns design method, known as the driving force approach. This study makes use of a four stage methodology and those stages are; sequence design, energy comparison, sensitivity comparison, and controllability comparison. In the first stage, a distillation columns sequence is designed based on the driving force algorithm. In the second stage, the energy consumption of the different designs is compared. In the third stage, the sensitivity of the different designs is compared and in the final stage the relative gain array method is used to determine the interaction between the designs’ control loops. The methodology is applied to a five component hydrocarbon mixture. Results showed that while the driving force design is the most energy efficient and robust, it does not have the best controllability.

Relative gain analysis of energy efficient hydrocarbon separation sequence

As there is presently insufficient information on the relation between sequencing method and controllability, this study is aimed to explore such relation between the driving force sequencing method and controllability. The methodology used consists of three stages; sequence synthesis, energy comparison, and controllability comparison. In the first stage, an energy efficient distillation columns sequence is synthesised using the driving force method, and other sequences are synthesised for comparison purposes. In the second stage, their energy usages are compared. In the third stage, relative gain array method is used to determine the controllability; the interaction between control loops in a sequence. The methodology is applied to a four component hydrocarbon mixture. Results showed that the sequence with the best controllability is the one synthesised based on the driving force approach.

Adaptation of Control Structure Design Methods to an Industrial Plant Engineering Workflow

Methods of systematic control structure design are adapted to suit industrial workflow of plant design and engineering in the chemical and process industry. The applied methods include a systematic step-wise design methodology and the concept of self-optimizing control. Implementation of these methods is performed in a commercial software framework that consists of Aspen Plus and MatLab. The control structure design methodology of an industrial sequence of heat-integrated distillation columns is presented as a case study.

A systematic method to synthesize all dividing wall columns for n‐component separation—Part I

We present an easy‐to‐use step‐wise procedure to synthesize an initial‐dividing wall column (i‐DWC) from any given n‐component basic distillation column sequence or its thermally coupled derivative. The procedure to be used is dependent on the nature of the distillation column sequence that is to be converted into a DWC, and comprises of an intuitive set of steps that we demonstrate through examples. It is noteworthy that, even for a ternary distillation, 15 potentially useful DWCs, some of which had been missing from the literature, have now been identified. This work significantly expands the search space of useful DWCs to separate any given multicomponent mixture. © 2017 American Institute of Chemical Engineers AIChE J, 64: 649–659, 2018

Simplifying and synthesizing practical four-product dividing wall column configurations

The fully thermally coupled distillation column for four components mixture separation is shown to be energy efficient compared to conventional distillation column sequence. However, it has not been implemented in practice as the form of four-product dividing wall column (FPDWC) because inherent three pairs of vapor and liquid splits increase the complexity and operation difficulty of this equipment. Thus it is necessary to reduce the vapor and liquid split number in order to promote its industrial application. In the present work, three heuristics were proposed to simplify the internal structure of FPDWC, which could be used separately or simultaneously. In order to provide a criterion for energy requirement comparison, minimum vapor flow diagram (Vmin) was employed and shown to be an effective tool to analyze the feasibility of each simplified configuration. Compared to the complex Petlyuk arrangement, these derived practical configurations use less partition walls without energy penalty. To summarize, a flowchart was developed to synthesize configuration with least design and operation effort by employing the proposed heuristics. Two industrial mixtures were taken as examples to validate its effectiveness.

Design and optimization of dimethyl oxalate (DMO) hydrogenation process to produce ethylene glycol (EG)

In this work, the steady state design of ethylene glycol (EG) production process by the dimethyl oxalate (DMO) hydrogenation is investigated. In comparison with the conventional ethylene oxide hydration process for EG production, this novel process provides better conversion and selectivity. The DMO hydrogenation process is comprised of a reaction section and a sequence of distillation columns as separation section. In reaction section, DMO is dissolved in methanol, and this DMO solution is then reacted with hydrogen to become EG and side products. Then, the raw product stream is fed into the sequence of distillation columns to obtain the EG product stream at the specified purity. After the initial process design is completed, the DMO hydrogenation process is optimized to obtain the optimal design with the minimum total annual cost (TAC). During process optimization, it is found that the mole ratio of hydrogen to DMO (HDMR) has global influences on TAC, and thus it is the last variable to be optimized. In this paper, the optimal case with HDMR=40 is obtained through optimization.

Hydrocarbon mixture fractionation direct sequence retrofitting and feed condition sensitivity analysis

The objective of this paper is to present the retrofit analysis for the hydrocarbon mixture (HM) direct sequence fractionation process and to analyse the process sensitivity with respect to feed conditions. To perform the study and analysis, the energy efficient HM separation process methodology has been developed. The methodology consists of four hierarchical steps. In the Step 1, a simple and reliable short-cut method of process simulator (Aspen HYSYS) is used to simulate a direct HM sequence. The energy used to recover individual fractions in the base sequence is analysed and taken as a reference. In the Step 2, an optimal HM sequence is determined using driving force method. All individual driving force curves for all adjacent components are plotted and the optimal sequence is determined based on the plotted driving force curves. Once the optimal HM sequence has been determined, the new optimal sequence is then simulated in Step 3 using a simple and reliable short-cut method (using Aspen HYSYS), where the process sensitivity and energy used in the optimal HM sequence are analysed, the process sensitivity of optimal HM sequence is compared with the other three different sequences by changing their feed conditions. Better sensitivity sequence was achieved when compared optimal sequence with the other three sequences in Step 4, the sequence determined by the driving force method has better sensitivity compared to the three other sequences as well as less energy requirement. All of these findings show that the methodology is able to design better sensitivity and minimum energy distillation column sequence for HM fractionation process in an easy, practical and systematic manner.

Optimal retrofit of natural gas liquids separation direct sequence and feed condition sensitivity analysis

The objective of this paper is to present the retrofitting analysis for the direct sequence natural gas liquids (NGLs) separation process and to analyse the process sensitivity with respect to feed conditions. To perform the study and analysis, the energy efficient NGLs separation process methodology is developed. Hence, the methodology consists of four hierarchical steps. In Step 1, a simple and reliable short-cut method for distillation column design of process simulator (Aspen HYSYS) is used to simulate a base (direct) NGLs sequence. The energy used to perform the separation is obtained that will be used for comparison purpose. In the Step 2, an optimal NGLs sequence is determined using driving force method. All individual driving force curves for all adjacent components are plotted and the optimal sequence is determined based on the plotted driving force curves. The optimal sequence is then simulated in Step 3 using a simple and reliable short-cut method (using Aspen HYSYS), where the energy used in the optimal NGLs sequence is analysed. Finally, the energy and sensitivity used in the optimal NGLs sequence is compared with the base sequence in Step 4. Several case studies involving several sequences have been used to test the performance of the developed methodology. A maximum energy saving of 11.7 MW was achieved when compared with the optimal (driving force) sequence with the direct sequence. For sensitivity analysis, the results show that the driving force sequence has the best sensitivity compared to other sequences. These findings show that the developed methodology is not only able to design energy efficient distillation columns sequence but also better process sensitivity with respect to the feed conditions for NGLs separation process in an easy, practical and systematic manner.

Study of thermally coupled distillation systems for energy-efficient distillation

Distillation is one of the most widely used separation unit operations in process industries, although it is quite energy intensive. In many cases, the enormous energy requirements for distillation make it economically infeasible to carry out the separation. Thermally coupled distillation system (TCDS) is an advanced distillation method that provides significant energy savings of about 30% as compared with conventional distillation column sequences. The most well-known TCDS sequence, the Petlyuk configuration, has some operational challenges due to bidirectional vapour flow, which makes its implementation difficult in two-column mode. To overcome these limitations, a number of unidirectional vapour flow configurations have been proposed in the literature. The work on simulation analysis for such configurations is limited. In this paper, simulation models for two such configurations are developed, analyzed and compared with the Petlyuk and conventional distillation column sequences for separation of equimolar mixture of benzene–toluene–ethylbenzene.

SUSTAINABLE ENERGY EFFICIENCY DISTILLATION COLUMNS SEQUENCE DESIGN OF AROMATIC SEPARATION UNIT

Distillation operations became a major concern within sustainability challenge, which it becomes a primary target of energy saving efforts in industrially developed countries. However, there is still one problem, which is how do we improve the energy efficiency of the existing distillation columns systems by considering the sustainability criteria without having major modifications. Therefore, the objective of this paper is to present new improvement of existing methodology by including a sustainability analysis to design an optimal sequence of energy efficient distillation columns. Accordingly, the methodology is divided into four hierarchical sequential stages: i) existing sequence sustainability analysis, ii) optimal sequence determination, iii) optimal sequence sustainability analysis, and iv) sustainability comparison and design modification. The capability of this methodology is tested in designing an optimal sustainable energy efficient distillation columns sequence of aromatics separation unit using a simple and reliable short-cut method within Aspen HYSYS® simulation environment. The energy and sustainability analysis is performed and shows that the optimal sequence determined by the driving force method has better energy reduction with total of 6.78 % energy savings and 0.16 % sustainability reduction compared to existing sequence with. In addition, the economic analysis shows that the return of investment of 3.10 with payback period of 4 months. It can be concluded that, the sequence determined by the driving force method is not only capable in reducing energy consumption, but also has better sustainability index for aromatic separation unit.

A formulation methodology for multicomponent distillation sequences based on stochastic optimization

Based on stochastic optimization strategy, a formulation methodology is proposed for synthesizing distillation column sequences, allowing more than one middle component as the distributing components between a pair of key components in the non-sharp split. In order to represent and manipulate the distillation configuration structures, a new coding procedure is proposed in the form of one-dimensional array. Theoretically, an array can represent any kind of split (non-sharp and sharp). With the application of a binary sort tree approach, a robust flow sheet encoding and decoding procedure is developed so that the problem formulation and solution becomes tractable. In this paper, the synthesis problem is formulated as a mixed-integer nonlinear programming (MINLP) problem and an improved simulated annealing approach is adopted to solve the optimization problem. Besides, a shortcut method is applied to the evaluation of all required design parameters as well as the total function.

ENERGY EFFICIENT DISTILLATION COLUMNS ANALYSIS FOR AN AROMATIC SEPARATION PROCESS

Energy savings is a major challenge in distillation operations. However, there is still one problem, which is how do we improve the energy efficiency of the existing distillation column systems without major modifications. Recently, a new energy efficient distillation columns methodology that will be able to improve energy efficiency of the existing separation systems without having major modifications has been developed. Therefore, the objective of this paper is to present a new improvement of the existing methodology by designing an optimal sequence of energy efficient distillation columns using a driving force method. Accordingly, the methodology is divided into four hierarchical sequential stages: i) existing sequence energy analysis, ii) optimal sequence determination, iii) optimal sequence energy analysis, and iv) energy comparison and economic analysis. The capability of this methodology is tested in designing an optimal synthesis of energy efficient distillation columns sequence of an aromatics separation unit. The existing aromatics separation unit consists of six compounds (Methylcyclopentane (MCP), Benzene, Methylcyclohexane (MCH), Toluene, m-Xylene and o-Xylene) with five direct sequence distillation columns being simulated using a simple and reliable short-cut method and rigorously tested within an Aspen HYSYS® simulation environment. The energy and economic analyses show that the optimal sequence determined by the driving force method has a better energy reduction with a total of 6.78% energy savings and a return of investment of 3.10 with a payback period of 4 months. It can be concluded that, the sequence determined by the driving force method is not only capable in reducing energy consumption, but also has a better economic cost for an aromatic separation unit

Comparative Study of Multicomponent Distillation Static Estimators Based on Industrial and Rigorous Model Datasets

The comparative study of static estimators (soft sensors) for a multicomponent distillation process based on the industrial and calibrated rigorous model datasets is considered. The sequence of distillation columns of an FFC unit is analyzed as an industrial case study. The contribution of the paper is to develop a method aimed at incorporating a priori knowledge about process in terms of rigorous models for static estimator design when the training sample is small and contains measurement errors. The superiority of a constrained optimization approach for SE design over conventional robust M -estimator is reported. The system of constraints is derived from a calibrated rigorous model of an industrial plant.

Energy Efficiency Improvement in the Natural Gas Liquids Fractionation Unit

The objective of this paper is to present the study and analysis of the energy efficiency for the natural gas liquids (NGLs) fractionation sequence by using driving force method. To perform the studies and analysis, the energy efficient NGLs fractionation plant methodology is developed. Hence, the methodology consists of four hierarchical steps; Step 1: Existing Sequence Energy Analysis, Step 2: Optimal Sequence Determination, Step 3: Optimal Sequence Energy Analysis and Step 4: Energy Comparison. The capability of this methodology is tested in designing an optimal energy efficient distillation columns sequence of NGLs fractionation unit. By using the driving force method, maximum of 21 % energy reduction is able to be achieved by changing the sequence of NGLs fractionation unit. It can be concluded that, the sequence determined by the driving force method is able to reduce energy used for NGLs fractionation. These findings show that the methodology is able to design energy efficient distillation columns for NGLs fractionation sequence in an easy, practical and systematic manner.

A design procedure for heat-integrated distillation column sequencing of natural gas liquid fractionation processes

The separation of NGL (natural gas liquids) in gas processing is energy-intensive, requiring systematic process design and optimization to reduce energy consumption and to identify cost-effective solutions for the recovery valuable hydrocarbons. As NGL fractionation processes require a sequence of distillation columns to separate multi-component mixtures the determination of optimal energy-efficient distillation sequences and operating conditions is not a simple task. A design methodology is proposed in this study in which the process simulator Aspen HYSYS® is linked with an optimization algorithm available in MATLAB®. The proposed methodology involves a procedure where in the first step possible distillation sequences are screened using a short-cut distillation column model. In the second step a few selected and promising candidate distillation sequences are further simulated and optimized, again using the same short-cut model. Finally, rigorous simulations are used to validate and confirm the feasibility of the optimal designs. A case study is presented to demonstrate the applicability of the proposed design framework for the design and optimization of NGL fractionation processes in practice.

Sustainable energy efficient distillation columns sequence design of hydrocarbon mixtures separation unit

Distillation operations became a major concern within sustainability challenge, which it becomes a primary target of energy saving efforts in industrially developed countries. However, there is still one problem, which is how do we improve the energy efficiency of the existing distillation columns systems by considering the sustainability criteria without having major modifications. Recently, a new energy efficient distillation columns methodology that will able to improve energy efficiency of the existing separation systems without having major modifications has been developed. However, this developed methodology was only considered the energy savings without taking into consideration the sustainability criteria. Therefore, the objective of this paper is to present new improvement of existing methodology by including a sustainability analysis to design an optimal sequence of energy efficient distillation columns. Accordingly, the methodology is divided into four hierarchical sequential stages: i) existing sequence sustainability analysis, ii) optimal sequence determination, iii) optimal sequence sustainability analysis, and iv) sustainability comparison. In the first stage, a simple and reliable short-cut method is used to simulate a base (existing) sequence. The sustainability index of the base sequence is calculated and taken as a reference for the next stage. In the second stage, an optimal sequence is determined by using driving force method. All individual driving force curves is plotted and the optimal sequence is determined based on the plotted driving force curves. Then, by using a short-cut method, the new optimal sequence is simulated and the new sustainability index is calculated in the third stage. Lastly, in the fourth stage, the sustainability index for both sequences (base and optimal) is compared. The capability of this methodology is tested in designing an optimal sustainable energy efficient distillation columns sequence of hydrocarbon mixtures separation unit. The existing hydrocarbon mixtures separation unit consists of eleven compounds (propane, i-butane, n-butane, i-pentane, n-pentane, n-hexane, benzene, cyclohexane, n-heptane, toluene, and n-decane) with ten indirect sequence distillation columns is simulated using a simple and reliable short-cut method and rigorous within Aspen HYSYS® simulation environment. The energy and sustainability analysis is performed and shows that the optimal sequence determined by the driving force method has better energy reduction with total of 4.64 % energy savings and sustainability reduction of 4.78 % based on existing sequence. It can be concluded that, the sequence determined by the driving force method is not only capable in reducing energy consumption, but also has better sustainability index for hydrocarbon mixtures separation unit.

Optimal Synthesis of Energy Efficient Distillation Columns Sequence for Hydrocarbon Mixture Separation Process

Abstract The objective of this paper is to present the study of the optimal synthesis of energy efficient distillation columns (EEDCs) sequence of hydrocarbon mixture separation process by using driving force method. In order to perform the study and analysis, the EEDCs sequence methodology is developed. Accordingly, the methodology consists of four hierarchical steps; Step 1: Existing Sequence Energy Analysis, Step 2: Optimal Sequence Determination, Step 3: Optimal Sequence Energy Analysis, and Step 4: Energy Comparison. The capability of this methodology is tested in designing minimum energy distillation column sequence for hydrocarbon mixture separation process. The results show that the maximum of 18% energy reduction was able to achieve by changing the sequence suggested by the driving force method. It can be concluded that, the sequence determined by the driving force method is able to reduce energy used for hydrocarbon mixture separation process in an easy, practical and systematic manner.