Distillation Column Sequences Research Articles

Investigation on Distillation Column Sequence and Heat Integration Effects in Methanol to Propylene Separation Unit: An Economic Optimization Study Based on Pinch and Exergy Analysis

Investigation on Distillation Column Sequence and Heat Integration Effects in Methanol to Propylene Separation Unit: An Economic Optimization Study Based on Pinch and Exergy Analysis

Optimization and design of a new column sequencing for crude oil distillation at Basrah refinery

Abstract The utilization of distillation stands as a predominant separation method within the chemical and petroleum industries, prominently influencing operational costs and environmental impact due to energy consumption. Enhancing energy efficiency holds paramount significance in elevating the sustainability and overall efficacy of distillation operations. Within this study, we introduce an innovative approach termed “marginal vapor flow (MVF)” to optimize the distillation column sequence for crude oil processing, focusing on the third distillation unit at the Basra Refinery. This research evaluates diverse column designs through streamlined simulations using Aspen HYSYS V11 software. The study determines total energy consumption as a benchmark, comparing it against the optimal sequence recommended by the MVF methodology. A novel application of the downward reduction equation to crude oil guides the selection of light and heavy components. Key findings from this comprehensive analysis showcase the potency of combining MVF with Aspen HYSYS for optimizing crude oil distillation column sequences. Aspen HYSYS, a widely recognized process simulation tool, accurately represents distillation processes. Simultaneously, MVF facilitates the determination of optimal column sequences based on marginal vapor flow rates. Notably, the results reveal that within the studied sequences, sequence 9 exhibits the lowest total MVF of (1393.4 kmol/h), signifying its optimality, while sequence 2 displays the highest total MVF of (4827.3 kmol/h), representing the least favorable scenario. Simulation of the optimal sequence derived through the MVF approach exhibits a remarkable 35% reduction in energy consumption compared to real-life operations. Conversely, simulating the least favorable sequence demonstrates a substantial 32% increase in energy consumption compared to actual operations. This study underscores the pivotal role of MVF methodology in optimizing distillation sequences for enhanced energy efficiency, providing actionable insights for refining operations to significantly reduce energy consumption and operational costs while advancing sustainability goals.

A hybrid deterministic-stochastic algorithm for the optimal design of process flowsheets with ordered discrete decisions

This work presents a hybrid stochastic-deterministic algorithm for optimal design of process flowsheets, i.e., finding the optimal design variables and operating conditions of multiple interconnected units using rigorous phenomenological chemical engineering models. Unlike previous studies that propose hybrid deterministic and stochastic algorithms in sequential and nested arrangements, the present work proposes a parallel configuration to perform the hybridization. The proposed hybrid algorithm combines a stochastic method (SM) with the deterministic Discrete-Steepest Descent Algorithm with Variable Bounding (DSDA-VB). The SM and DSDA-VB strategies interact in parallel by exchanging new feasible solutions identified by the SM and improved search bounds determined by the DSDA-VB. The proposed method is illustrated using a thermally coupled system and a sequence of reactive, extractive, and traditional distillation columns. The results indicate that the proposed algorithm outperforms the traditional Differential Evolution with Tabu List (DETL) algorithm, showing faster and improved convergence.

A novel “feed-backward” control structure for on-demand control of distillation column sequences

The typical conventional plantwide control structure sets the flow rate of the fresh feed entering the process. Sometimes marketing or safety requirements dictate that the flowrate of the product leaving the process must be flow controlled. This structure is called “on-demand.” Important examples of chemicals that must be supplied on an “as-needed” basis include hydrogen, oxygen, synthesis gas, toxic hydrogen cyanide and explosive nitrotoluene. Since the output flow is fixed in an on-demand control structure, the material balance loops controlling liquid levels and gas pressures must work their way back upstream through the process to eventually adjust the fresh feed streams. A novel on-demand control structure is developed in this paper that reduces peak dynamic disturbances throughout the process by immediately changing upstream flow rates in a “feed-backward” manner when the product flow rate is changed.

Optimal Sequencing of Multicomponent Distillation Columns by Rigorous Calculation Methods

Optimal Sequencing of Multicomponent Distillation Columns by Rigorous Calculation Methods

A simple screening method for distillation sequence of thermally coupled dividing wall column: distillation sequence morphological analysis method (DSMAM)

AbstractBACKGROUNDDistillation is a separation process with a high energy consumption. Therefore, energy‐saving optimizations of the distillation process have become particularly significant. However, developing methods to quickly choose the best energy‐saving distillation sequence for the separation of multiple components has become a key problem.RESULTSIn this paper, the Distillation Sequence Morphometry Analysis Method (DSMAM) was established to quickly screen energy‐saving and efficient distillation sequences and was integrated with a Dividing‐wall column (DWC) device, which has more industrial significance. Meanwhile, an evaluation and screening index η of separated multicomponent energy‐saving distillation sequences was proposed. Finally, based on the DSMAM, and combined with Microsoft Visual Basic 6.0 (VB) and Aspen Plus V11 (Aspen) software, a set of distillation sequence screening and evaluation programs of four‐component separation systems was generated. The distillation column sequence with high thermodynamic efficiency and the energy‐saving coupling structure of distillation were obtained quickly and accurately.CONCLUSIONThis program was applied to the separation of the n‐butane‐benzene‐n‐heptane‐n‐nonane system. It was able to quickly obtain the first three energy‐saving distillation sequences without thermal coupling and the first three energy‐saving distillation sequences in the search space. The direct‐thermal coupling distillation sequence of the energy‐saving fluid was integrated and coupled, providing a preliminary design reference for industrial design and application. © 2022 Society of Chemical Industry (SCI).

Optimal sequencing of conventional distillation column train for multicomponent separation system by evolutionary algorithm

Abstract The best structure of multicomponent separation techniques can be obtained using optimal distillation sequencing. Because distillation sequences contribute significantly to the fixed and operational cost of the entire chemical process, developing a systematic approach for choosing the most appropriate and economic distillation sequences becomes an important field of study. Due to its high dimensional space and combinatorial nature, synthesis of the optimal conventional distillation column sequence is a tough problem in the field of process plant development and optimization. A novel method for the synthesis of an optimal conventional distillation column sequence is suggested in this study. Genetic algorithm, an evolutionary algorithm is at the heart of the proposed method. The Total Annual Cost (TAC) is the main basis used to evaluate alternative configurations. To estimate the total cost of each sequence, rigorous methods are used to design all columns in the sequence. The proposed method’s performance and that of the conventional quantitative approach are compared using the results of a five component benchmark test problem used by researchers in this field. According to the comparison results, the suggested algorithm outclasses the other methods and is more adaptable than other existing approaches.

Thermodynamics fundamentals and energy efficiency for the separation and high-valued utilization of Fischer–Tropsch heavy oil

The development trend of Fischer–Tropsch (F–T) technology is to develop high value-added products. The separation of linear α-olefins with low cost is an effective method. Nevertheless, the lack of thermodynamic data and the huge energy consumption are the two main problems restricting the development of the separation process. The thermodynamic data of the key components (1-dodecene and n-dodecane) in the F–T product were measured. The Wilson binary interaction parameters of the key components were obtained. Next, one traditional distillation column sequence and two dividing wall column (DWC) sequences were designed to separate the F–T heavy oil to obtain narrow fractions with different carbon numbers. Then, the obtained fractions of C10 and C12 were simulated to obtain 1-decene and 1-dodecene, respectively. There was a traditional distillation and a differential pressure thermal coupling distillation process. When separating 95.0% purity 1-decene and 1-octene, the direct DWC process and differential pressure thermal coupled distillation are an excellent combination, which can reduce the energy by 33.1% (i.e., 11,286 kW) and total annual cost by 15.9% (i.e., 3.96 × 106 $) compared with traditional distillation.

Structural considerations in zeotropic distillation sequences with multiple feeds

The separation of multiple feed streams with some common components using sequences of distillation columns produces a rich space of alternatives that must be considered. In this work, we present the main structural characteristics of sequences generated when we want to take advantage of the synergies of common components in multiple feed streams to reduce both, energy consumption and the total number of distillation columns. In general, the sequence of separation tasks of the whole system can be obtained from the sequences of separation tasks of each one of the feeds. However, the integration in actual columns is not so straightforward and we must consider aspects like the optimal location of feeds in multiple-feed columns; and the alternatives of integration of common sub-mixtures (when possible) in actual columns. Besides, the optimal sequence of separation tasks for each feed is not necessarily the same when all of them are considered simultaneously. We show that the minimum number of actual columns, without considering further intensification, depends on the number of components in each feed and on the possibilities of integration of common sub-mixtures, so we extend the concepts of regular and basic column sequences to deal with these new situations. The examples show the potential savings in energy and number of columns compared to maintain isolated each feed; mixing the feed streams or an incorrect integration.

Design and optimization of distillation column sequencing for the GTL process

Gas to liquid (GTL) is one of the main processes that liquefied natural gas through chemical conversion into synthetic crude that can be upgraded and separated into different useful hydrocarbons. The present study has been carried out to optimize the distillation column configuration and applied it to the GTL distillation unit. The distillation simulation code has been developed in two main parts, shortcut and rigorous based on inside–out algorithm. A modular design approach is presented in which the code is developed in only one computational environment. Compared to the existing methods, the uniform code avoids time-wasting data transmission between different commercial software. Therefore, the developed code includes all three main steps, generation, simulation and optimization, which are interconnected to achieve the best sequence according to the objective function. The genetic algorithm is utilized to minimize the hybrid TAC function that checks products specifications simultaneously. The results demonstrate the capacity of direct configuration that performances the best overall evaluation parts of TAC, operating costs, capital costs, and exergy losses, therefore it reduces up to 26% in operating cost compared with indirect configuration which is the most commonly used sequence in GTL plant.

Simulation of Methoxy methyl heptane (MMH) production using unisim design R460.1

Various fuel additives are employed till now like ethanol, ethyl tertiary butyl ether (ETBE), MTBE, Di Isopropyl alcohol (DIPA) etc. after the phase-out of lead-based compounds to enhance the octane number of fuel. MMH is suggested as an alternative to methyl tertiary butyl ether (MTBE) and similar ethers since they causes groundwater contamination. The liquid phase reversible reaction of methanol (MHOH) with 2-methyl1-heptene (MH) produces MMH. But there is an undesirable reaction also to form Dimethyl ether (DME) and 2-methyl-2-heptanol (MHOH). The process of MMH production is simulated using Unisim Design software R460.1. Conventionally, MMH is produced through a reactor and three distillation column sequences for yielding high purity MMH. This reactor-column sequence requires either high MH recycle or large-sized reactor to have the desired yield. Both results in large capital and operating costs. A reactive distillation concept can tackle these constraints with reactor and distillation in a single column known as reactive distillation column (RDC).The feasibility of RDC and analysis of the process can be observed using Unisim Design software since pilot plants are costly for this type of RD process. The simulation of the process using different test bed Unisim R460.1 is not explored yet.

Natural gas liquid (NGL) distillation process using driving force and thermal pinch analysis methods: Energy and economic assessment

Distillation column is one of the effective unit operations that is commonly used to separate chemical mixtures. The only drawback of this separation process is its huge energy consumption especially for a multicomponent separation process which involves a series of distillation columns. Therefore, an optimal sequence must be determined to address the issue. This research proposes the methodology to determine the optimal sequence of distillation columns by using driving force method. Then, thermal pinch analysis is applied to obtain further energy saving in the process. The case study selected is a distillation process to recover 5-component of natural gas liquid (NGL) mixture. Based on the input data, the driving force sequence is determined first and simulated together with a conventional sequence (direct sequence). Then, the extracted data from the simulation will be used for thermal pinch analysis via problem table algorithm (PTA). From the results of PTA, energy consumption between both sequences were compared including the energy consumption before and after the thermal pinch analysis. In addition, economic analysis has been performed as well to indicate which sequence has lower capital and operating costs based on the proposed heat exchanger network (HEN). According to the results, the combination of the driving force and thermal pinch analysis methods has successfully recorded 48% of energy savings and operating cost, and 58.2% capital cost saving compared to the conventional sequence (direct sequence). Therefore, it can be said that the proposed framework has a great potential to be employed towards the process and economic feasible distillation process.

Strategies for separating pressure sensitive binary azeotropes

The separation of azeotropic mixtures, particularly, pressure sensitive azeotropes is intriguing, challenging, and inevitable in chemical industries in comparison to pressure insensitive azeotropic mixtures. The main bottleneck for separating pressure sensitive azeotropes lies in the pressure selection and sequencing of distillation columns. A conundrum in pressure swing distillation for both minimum and maximum boiling azeotropes primarily about the feasibility of column configurations has been discussed in this work. The two column configurations, Low pressure Column-High Pressure Column (LPC-HPC) and High Pressure Column-Low Pressure Column (HPC-LPC) are found to be dependent on the feed composition, type of azeotrope (whether, minimum or maximum), and the effect of pressure on azeotropic composition. This article has explored concomitantly pressure swing distillation technique (continuous one) and the effect of various feed compositions on the column sequencing and process feasibility. A comprehensive strategy for both minimum and maximum boiling azeotropes has been proposed depending upon the effect of pressure on azeotropic composition. Two example case studies have been also presented in support of the proposed strategies for pressure swing distillation technique.

Energy saving potential of 6-component aromatic mixture via Energy Integrated Distillation Columns Sequence (EIDCS) method

Distillation column is a well-known unit operation in chemical and petrochemical industries for an intended separation task. However, the energy usage still becomes a problem particularly for a multicomponent system of distillation columns sequence. Therefore, this research aims to investigate the applicability of Thermal Pinch Analysis to be employed in a distillation columns sequence to solve the problem. The method is complemented by the sequencing method of Driving Force which leads to a novel method namely Energy Integrated Distillation Columns Sequence (EIDCS). This systematic method has been designed for optimal distillation columns sequence and further energy saving by Thermal Pinch Analysis. The Driving Force Sequence was firstly determined by the use of Driving Force Plot. Then the shortcut and rigorous simulations have been carried out and the resulting data were extracted for Thermal Pinch Analysis at a fixed value of ΔTmin at 10 °C. Next, the Problem Table Algorithm (PTA) was constructed to indicate the possible energy saving for the distillation columns sequence. Finally, the proposed Heat Exchanger Network (HEN) via Grid Diagram that satisfies the energy requirement was constructed. A case study of 6-component Aromatic Mixture has been selected to evaluate the proposed EIDCS method in this study.

Control and energy analyses of a driving force-based aromatic mixture distillation columns sequence

To minimize the energy usage of distillation systems, past researchers have developed algorithms that exploit the driving force of distillation, which is the difference in vapour and liquid fractions due to relative volatilities. So far, little is known about the degree of controllability of the energy efficient solutions. This paper aims to ascertain that idea by applying a simple methodology on a common mixture as the case study. The methodology is made up of four stages: (1) feed information gathering, (2) sequence determination, (3) energy analysis and (4) controllability analysis. The controllability was analysed in terms of input-output interaction and resiliency using RGAno and MRI, respectively. From the application, it has been found that the sequence determined using driving force algorithm is the most optimal sequence overall, measured by the use of a multi-objective function.

Design and optimization of distillation column sequencing for NGL fractionation processes

NGL fractionation is one of the most energy-intensive facilities in hydrocarbon processing plants playing an important role in the petrochemical supply chain. Innovative schemes for multicomponent distillation processes made the opportunity to attain more justifiable fractionation processes. The current study presents a systematic procedure to design and optimize both simple and complex distillation schemes based on the separation matrix approach and applies it to a NGL feedstock. A modular design approach is presented for the ultimate rigorous evaluation. The genetic algorithm with a hybrid objective function that minimizes the TAC and checks products specifications simultaneously carries out optimization. The results demonstrate the capability of complex distillation sequences in process improvements, reducing costs and saving energy in NGL fractionation plants resulting in reductions of up to 3.5% in annual operating costs, which is very significant bearing in mind the huge NGL fractionation scale of operation.

Optimal configuration of ternary distillation columns using heat integration with external heat exchangers

The subject of energy saving in distillation column sequencing is of critical importance. Heat integration in a multicomponent separation can be industrialized by saving considerable energy and cost. In this work, external heat-integrated distillation column with external heat exchanger has been studied and the annual cost function has been optimized using Genetic Algorithm. Introducing the layout and binary matrices enabled the investigation of all possible locations for the heat exchanger arrangement successfully. Moreover, exchangers heat loads and compressors pressure, have also been considered as optimization variables. Benzene, toluene, xylene and n-alkanes, separations have been studied as case studies. It has been demonstrated that the proposed optimization method in the alkane separation case decreased the total annual cost by 22.6% in comparison with the proposed thermally coupled distillation sequence columns. The heat integration of external heat exchangers in an external heat-integrated distillation column configuration and the proposed dived-wall column resulted in decreasing the total annual cost by 17% and 39% respectively, in comparison with conventional distillation columns.

Interaction and performance analysis of a ternary mixture distillation process

The objective of this study was to analyse the controllability of a driving force-based distillation columns sequence for the separation a benzene, toluene, and p-xylene mixture. Primarily, a methodology for this study was constructed, which consisted of five hierarchical stages. In the first stage, all possible distillation columns sequences were synthesised. Then, the sequences were simulated under steady state conditions using Aspen HYSYS in the second stage. In the third stage, the input-output interactions of the sequences were analysed by using relative gain arrays (RGA). In the fourth stage, controller parameters were determined. Finally, in the fifth stage, the controllers’ responses were analysed using MATLAB. From this study, it was found that the driving force-based distillation columns sequence has better overall controllability than an alternative sequence.

Conceptual design of distillation columns sequence for separation of pentane and hexane from C5+ stream of LPG unit

ABSTRACTThe principal role of an LPG (Liquefied Petroleum Gas) unit is the separation of propane and butane from other products in a gas refinery. One of the other main products of the LPG unit is C5+ which is sold at the same price of crude oil after it is added into gas condensate. In this research, sixth refinery (Phases 15 and 16) of South Pars gas filed was selected as a case study example to find an efficient design for enriching the C5+ stream. Analysis of the C5+ stream exited from the LPG unit demonstrates that it contains more than 70 wt. % of valuable solvents such as pentane and hexane which are more expensive than crude oil. Therefore, the main goal of this research is to do calculations related to the separation of these solvents from the C5+ stream using the direct and indirect sequence of distillation columns. For this purpose, an optimum algorithm is recommended based on Fenske-Underwood-Gilliland (FUG) method in which design parameters (column pressure and reflux ratio) are optimized so that the objective function that represents the total annual cost (TAC) is minimized. Programming with MATLAB shows that the theory of the direct sequence of distillation columns is more economical than the indirect sequence (an annual income of 40,309,012$ is estimated with a fixed cost of 1,047,555 $). Economic calculations also revealed that the rate of return (ROR) and annual profit would be 38.48% and 650,000,000 $.year−1, respectively, if the optimal direct sequences of distillation columns are performed in all the gas refineries of South Pars.

Energy Integrated Distillation Columns Sequence (EIDC) of 5-Component Alcohol Mixture via Driving Force and Thermal Pinch Analysis Approach.

Energy Integrated Distillation Columns Sequence (EIDC) of 5-Component Alcohol Mixture via Driving Force and Thermal Pinch Analysis Approach.