Design Of Distillation Columns Research Articles

Rigorous design and economic optimization of reactive distillation column considering real liquid hold-up and hydraulic conditions of industrial device

The liquid hold-up in a reactive distillation (RD) column not only has a significant impact on the extent of reactions, but also affects the pressure drop and hydraulic conditions in the column. Therefore, the liquid hold-up would be a critical design factor for RD columns. However, the existing design methods for RD columns typically neglect the influence of considerable amount of liquid hold-up in downcomers owing to the difficulties of solving a large-scale nonlinear model system by considering downcomer hydraulics, resulting in significant deviations from actual situation and even operation infeasibility of the designed column. In this paper, a pseudo-transient (PT) RD model based on equilibrium model considering tray hydraulics was established for rigorous simulation and optimization of RD plate columns considering the liquid hold-up both in downcomers and column trays, and a steady-state optimization algorithm assisted by the PT model was adopted to robustly solve the optimization problem. The optimization results of either ethylene glycol RD or methyl acetate RD demonstrated that assuming all the liquid hold-up of a stage belonged to the tray will cause significant deviations in the column diameter, weir height, and the number of stages, which leads to not meeting the separation requirements and even operation hydraulic infeasibility. The rigorous model proposed in this study which considers the liquid hold-up both on trays and in downcomers as well as hydraulic constraints can be applied to systematically design industrial RD plate columns to simultaneously obtain optimal operating variables and equipment structure variables.

Vapor-Liquid Equilibrium of System Comprising Green Solvents: A Holistic Review

Abstract: The design and operation of distillation columns is based on vapor-liquid equilibrium data, which is a necessity for the chemical industry. In recent years, chemical industry has embraced green chemistry and sustainable development. Furthermore, green solvents are more environmentfriendly and cleaner than conventional solvents and thus offer a good alternative. Very limited work has been reported in the literature that focuses on the generation of isobaric/isothermal vapor-liquid equilibrium (VLE) data of systems comprising green solvents. In this paper, reported VLE data are explored for three emerging green solvents, such as cyclopentyl methyl ether (CPME), γ- valerolactone (GVL), and 2-methyltetrahydrofuran (2-MeTHF). Emerging green solvents have favorable environmental, health, and safety characteristics, making them attractive alternatives for a wide range of applications. The study focuses on two critical separations; the extraction of formic acid from Power-to-X chemical processes and purification of acetic acid from chemical synthesis or fermentation processes. Both processes are integral parts of the chemical industry's sustainable development. To facilitate these separations, accurate VLE data for these green solvents with acetic acid/formic acid systems are essential. The paper reviews literature related to VLE data for systems involving these green solvents. It provides insights into the experimental conditions, equipment, analysis methods, thermodynamic models, and error-minimizing functions used in the previous studies. The researchers can refer to this information as a useful reference prior to the VLE experimentation and modeling of systems comprising these three green solvents. Moreover, the paper presents an overview of recent research on green solvents and their applications, illustrating their versatility and potential for various industrial processes. Research efforts are needed to generate VLE data for green solvent systems and support the chemical industry in transitions towards more sustainable practices.

Design and operation of a packed pilot scale distillation column for tire pyrolysis oil: Towards the recovery of value-added raw materials

This work describes the key features involved in the design and operation of a pilot scale distillation column for the recovery of value-added products from tire pyrolysis oil (TPO), as part of the BLACKCYCLE project. The distillation unit was designed using engineering heuristic rules, simulated distillation (SimDist) data and Aspen Hysys ® modeling. The distillation plant consists of a packed column with a nominal throughput of 20 kg/h, and is classified at the fifth technology readiness level (TRL-5). The commissioning and results of long-term experimental campaigns for validation purposes are also presented. In this way, important information is gathered for the design of larger plants. The distillation unit was tested and validated using TPO produced from a pilot scale continuous single-auger pyrolysis plant. A first distillation was performed yielding a heavy fraction (HF-1) with properties suitable for carbon black production, while the light fraction (LF-1) includes the presence of value-added chemicals such as benzene, toluene, ethylbenzene and xylenes (BTEX) and limonene. The LF-1 was also used for a second distillation, producing a stream high in limonene at the bottom (HF-2), and another one high in BTEX compounds at the top (LF-2), which are valuable raw materials for polymer production and petrochemicals, respectively. The key results obtained here are expected to provide an outstanding impetus for the circular economy of complex streams such as end-of-life tires (ELTs) by combining pyrolysis and distillation technologies.

Enhancing Techno Economic Efficiency of FTC Distillation Using Cloud-Based Stochastic Algorithm

A liquefied petroleum gas plant facility (LPGPF) is a series of binary distillation columns used to separate natural gas into four alkanes: ethane, propane, butane, and pentane. The conventional distillation column design consists of three binary distillation columns and six heat exchangers to perform the process. Each heat exchanger consumes immense energy to heat up the reboiler and condense the distillate. There are several process technologies that can minimize distillation column energy consumption. In this research, a fully thermally coupled distillation column (FTCDC) was proposed to minimize energy consumption by reducing the number of heat exchangers and tray columns. An FTCDC has the capability to reduce capital expenditure, operational expenditure, and total annual cost (TAC). The complexity of the FTCDC arises from its process integration. In each column, the intersection composition depends on complex mass and energy balances at the column inlet and outlet and each tray. Process integration, including material recycling and heat recovery, increases the complexity significantly. Moreover, the decision variables are multi-intersection composition for each column to achieve optimum objective function, increasing the number and complexity of the computational load such that effective stochastic optimization algorithms are required. The proposed method was designed using a rigorous vapor liquid equilibrium (VLE) FTCDC model and incorporated with recent stochastic optimization algorithms, such as a genetic algorithm, particle swarm optimization (PSO), an imperialist competitive algorithm, and a duelist algorithm, to determine hydrocarbon composition in the FTCDC intersection. To increase the efficiency and effectiveness of the FTCDC optimization design, cloud computing was utilized. The result was compared with conventional methods such as Fenske-Underwood-Gilliland, a Fenske-Underwood-Gilliland modification, and VLE. The optimization objective function is to minimize TAC with hydrocarbon composition in the FTCDC intersection as decision variables. The optimization using the VLE-PSO method reduces TAC up to 26.28%. All designs were validated using a rigorous model with Aspen HYSYS commercial software. This study's primary goal is to improve the performance of FTCDCs using stochastic algorithms and cloud-based computing capacity. The large amount of computation is handled by cloud-based computing resources, enabling reliability and durability.

Complementary role of large language models in educating undergraduate design of distillation column: Methodology development

This paper explores the integration of large language models (LLMs), such as ChatGPT, in chemical engineering education, departing from conventional practices that may not be universally accepted. While there is ongoing debate surrounding the acceptance of LLMs, driven by concerns over computational instability and potential inconsistencies, their inevitability in shaping our communication and interaction with technology cannot be ignored. As educators, we are positioned to play a vital role in guiding students toward the responsible, effective, and synergetic use of LLMs. Focusing specifically on distillation column design in undergraduate mass-transfer courses, this study demonstrates how ChatGPT can be utilized as an auxiliary tool to create interactive learning environments and simulate real-world engineering thinking processes. It emphasizes the need for students to develop critical thinking skills and a thorough understanding of LLM principles, taking responsibility for their use and creations. While ChatGPT should not be solely relied upon, its integration with fundamental principles of chemical engineering is crucial. The effectiveness and limitations of ChatGPT are exemplified through two case studies, showcasing the importance of manual calculations and established simulation software as primary tools for guiding and validating engineering results and analyses. This paper also addresses the pedagogical implications of integrating LLMs into mass transfer courses, encompassing curriculum integration, facilitation, guidance, and ethical considerations. Recommendations are provided for incorporating LLMs effectively into the curriculum. Overall, this study contributes to the advancement of chemical engineering education by examining the benefits and limitations of LLMs as educational aids in the design process.

Process intensification in bio-jet fuel production: Design and control of a catalytic reactive distillation column for oligomerization

Biojet-fuel represents a promising avenue for decreasing CO2 emissions within the aviation industry. Among different biojet-fuel production processes, the Alcohol-to-Jet (ATJ) process stands out as highly promising. Despite its potential, the ATJ process currently faces economic challenges due to low yields and high energy usage. This study introduces a strategy for enhancing the economic feasibility of the ATJ process through process intensification, specifically by incorporating a novel reactive distillation column in the oligomerization stage. This innovative process was evaluated and compared with its conventional counterpart. The total annual cost, eco-indicator 99, and individual risk were chosen as critical parameters for assessing the improvements in cost, environmental impact, and safety brought about by the reactive column. Additionally, control studies were conducted using both Proportional-Integral (PI) and Model Predictive Control (MPC) controllers to determine the feasibility of operating the reactive distillation column. The results suggest that the reactive distillation process offers 20 % cost savings, reduces environmental impact by 50 %, and lowers risk by 22 % when compared to the conventional process. In terms of control strategies, the study found that the catalytic column can be successfully operated using both traditional feedback control and more advanced techniques, such as model predictive control.

Intelligent Optimization Design of Distillation Columns Using Surrogate Models Based on GA-BP

The design of distillation columns significantly impacts the economy, energy consumption, and environment of chemical processes. However, optimizing the design of distillation columns is a very challenging problem. In order to develop an intelligent technique to obtain the best design solution, improve design efficiency, and minimize reliance on experience in the design process, a design methodology based on the GA-BP model is proposed in this paper. Firstly, a distillation column surrogate model is established using the back propagation neural network technique based on the training data from the rigorous simulation, which covers all possible changes in feed conditions, operating conditions, and design parameters. The essence of this step is to turn the distillation design process from model-driven to data-driven. Secondly, the model takes the minimum TAC as the objective function and performs the optimization search using a Genetic Algorithm to obtain the design solution with the minimum TAC, in which a life-cycle assessment (LCA) model is incorporated to evaluate the obtained optimized design solution from both economic and environmental aspects. Finally, the feasibility of the proposed method is verified with a propylene distillation column as an example. The results show that the method has advantages in convergence speed without sacrificing accuracy and can obtain an improved design solution with reduced cost and environmental impact. Compared with the original design using rigorous simulation, the TAC is reduced by 6.1% and carbon emission by 27.13 kgCO2/t.

Understanding the impact of reactive holdup on process intensification in the design of reactive distillation column

The commercial viability of reactive distillation as a front-runner industrial process intensification technique is limited by slow reactions. It is because the diameter established by the vapor-loading method restricts large holdup volumes (or catalyst amount) to accomplish the essential conversion. However, placing a large amount of catalyst on column trays necessitates either a high tray weir height (limited to excessive column pressure drop) or a large column diameter. This study aims to investigate an alternative design approach by increasing the column diameter beyond that required for vapor loading to retain a large holdup volume. Several combinations of tray weir heights and column diameters were studied and demonstrated through case studies for three industrial processes, and their optimal designs have been reported. High catalyst holdup volume enhanced energy efficiency and overcame hydraulic limitations despite requiring large diameter vessels. These design configurations with optimized catalyst holdup also resulted in improved process economics. Fabricating a wide column diameter is a good conservative engineering procedure considering safety aspects and better design control.

Optimized conditions for the design and operation of a vacuum distillation column for the purification of crude glycerol from biodiesel production

AbstractDue to the growth in global demand for biodiesel, there is a tendency for the volume of its main by‐product, glycerol, available on the market to increase. This has led to a search for new uses for this by‐product and the development of new processes that use glycerol as a raw material because it has wide industrial applications. However, to be used in many of these processes, the glycerol must go through a purification stage before reaching the purity required for the application (which can reach 99.7% w/w). Taking this into account, the optimization of the parameters for the main glycerol purification stage (vacuum distillation) is essential to reduce the cost of this stage as much as possible. In this article, optimization of the vacuum distillation column was carried out using an artificial neural network (ANN) and a genetic algorithm (GA) together. With the optimization, it was found that four theoretical stages of equilibrium (separation) is the optimal value, in economics terms, for the distillation column on an industrial scale, leading to better performance (in terms of glycerol purity) than patents that used a smaller number of theoretical stages and an equal performance in relation to the patents that used a greater number of stages, which in this case reduces the cost with the size of the column. This result helps to increase the financially viability of using glycerol as a raw material, which can make several processes cheaper, thus generating greater added value to this sustainable by‐product. © 2023 Society of Industrial Chemistry and John Wiley & Sons Ltd.

Co-process intensification in the synthesis and design of reactive double dividing-wall distillation columns

In most cases, the reactive single dividing-wall distillation column (R-SDWDC) and its corresponding conventional reactive distillation system (CRDS) fail to yield the best performance in the separations of reacting mixtures with unfavorable reaction kinetics and/or unfavorable thermodynamics properties. In this work, a novel methodology of co-process intensification is proposed for the synthesis and design of reactive dividing-wall distillation columns. The methodology leads to the establishment of a reactive double dividing-wall distillation column (R-DDWDC), and the included intermediate separating section plays a vital role in coordinating these two kinds of process intensification and consequently guarantees its optimum performance. In terms of two example systems involving the separations of the ideal quaternary reversible reaction with a somewhat unfavorable ranking of relative volatilities (A + B ↔ C + D with αA > αC > αB > αD) and the transesterification of methyl acetate with n-propanol, the proposed methodology is evaluated. The R-DDWDC is found to yield much better performance than the CRDS and R-SDWDC in the separations of the reacting mixtures with somewhat unfavorable ranking of relative volatilities, and such outcomes definitely corroborate the effectiveness and advantages of the proposed methodology for process development. Although the proposed methodology is developed solely based on the separations of the reacting mixtures with somewhat unfavorable ranking of relative volatilities, it is of great implication to the separations of the other reacting mixtures with unfavorable reaction kinetics and/or unfavorable thermodynamics properties.

Heterogeneous phase diagram and residue curve map for ethanol-water-ethyl acetate and ethanol-water-ethyl acrylate system

Heterogeneous phase diagram and residue curve map data are simulated using NRTL equation which are useful for design of heterogeneous Azeotropic distillation column. Simulated data are compared with experimental data.

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Criteria for optimization of the distillation process of the distillated liquor are qualitative composition of the liquor distillate, concentration of ethyl alcohol in the distillate and bard and specific flow rate of heating steam in the distillation column. These characteristics depend on the quality composition of the mash, the number and type of plates, the hydraulic mode of their operation, the temperature mode of the distillation process, the method of heating the column, the degree of decarbonization of the mash and the effectiveness of automation of control and monitoring of technological parameters. An important optimization factor is increase of the con-tact time of steam and mash on the column plates in order to achieve a phase state close to equilibrium. The authors proposed an energy-saving technology for distillation of the mash in the mode of controlled cycles of its delay and overflow, developed a design of distillation column for the implementation of the innovative method and hardware-technological scheme of inclusion it to work. Under production conditions, the optimal technological parameters and hydraulic operating modes of the experimental column of cyclic action are established. It is proved that the innovative way allows to prolong time of contact of steam and mash on each plate to 35—40 s and to reduce time of its overflow from plate to plate to 1.5—1.7 s, due to this the concen¬tration of ethyl alcohol in the distillate increased by 33% (up to 60% vol.), the column capacity — by 17% (from 15000 to 18000 dm3/h) and specific consumption of heating steam for distillation process decreased by 60% (from 25 to 10 kg/dl in terms of anhydrous alcohol, introduced to the feed plate). In order to achieve the above-mentioned indicators, it is sufficient to install 24 flake plates with variable free cross-secti¬on, which allows reducing the metal-intensity of the technological equipment.

Experimental evaluation of the performance of a cryogenic distillation system under offshore conditions

Cryogenic distillation is the most widely-used industrial method to produce liquid oxygen with high-purity. However, the distillation process in the sieve tray column is very sensitive to tilting and swing, which limits the application of cryogenic air-separation in marine and offshore infrastructures. In this paper, a small air-separation plant with dual-column distillation process was proposed to improve the distillation performance under the offshore conditions, and experiments were carried out under standard (no-tilting and stationary), tilting and swing conditions. A reduction factor of overall section efficiency is proposed to evaluate the influence of offshore conditions on the system performance. The results indicate that sieve tray column can maintain the distillation purity to a certain extent under offshore conditions within the range of 6° tilting and ±10° swing amplitude. Under severe tilting (6°) and swing (±10°-amplitude&11 s-period) conditions, the reduction factors were reduced to 0.592 and 0.590, respectively. Based on the experimental results, two correlations are presented to predict the reduction factor of section efficiency under different tilting angle and swing parameters, respectively, which provide engineering guidance for the design of cryogenic distillation column for offshore applications.

A new efficiency relaxation model for rigorous stage number optimization of distillation columns

Determining the optimal state number in distillation column design is a mixed-integer nonlinear programming (MINLP) problem, which is difficult to solve. One strategy to solve this problem is relaxing integer stage numbers into continuous variables and solving an easier nonlinear programming (NLP) problem. However, the existing relaxation model often converges to non-integer stage numbers or poor local optima in practical applications, which motivates this paper to develop a new relaxation model. The proposed relaxation model employs an interpolation function to relax the discrete decision on the existence of a stage by varying interphase mass and heat transfer rate between zero and equilibrium state. By adjusting a shape parameter in the interpolation function, the interpolation function shape and its penalty extent of non-integer stage can be manipulated. The results of three distillation column optimization cases show that the proposed model can effectively avoid converges to non-integer stage numbers or poor optima.

Intensification of Heat and Mass Transfer in a Diabatic Column with Vortex Trays

We used vortex contact devices that we developed and investigated to make a new design of an alcohol diabatic distillation column with heat exchange pipes (as the reflux condenser) passing through concentrating section trays. In the column, ascending vapors partially condensed on the surface of vertically installed heat exchange tubes, forming a reflux. The reflux was then mixed with the draining liquid flow in the vortex contact devices placed on the trays. Heat was removed from the column through the boiling of the draining water film along the inner surface of the heat exchange pipes. We compared both diabatic and adiabatic columns fitted with the developed vortex contact devices on the trays. The proposed innovative contact system allows increasing productivity, reducing column dimensions and steam- and heat-transfer medium consumption, and increasing separation efficiency. Dependences for calculating the gas content, hydraulic resistance, and interphase surface required for designing the vortex contact devices of the proposed unit trays are presented.

An inherently safer development approach for thermally coupled distillation sequences: Application in hazardous chemical separation

Process safety is always a core issue in chemical industry, which is conventionally not taken into consideration during the conceptual design stage of a process flowsheet. Distillation handles more than ninety percent of the separation and purification tasks of hazardous chemicals and accounts for no less than forty percent of the total energy consumption. Therefore, this work presents an inherently safer synthesis framework for thermally coupled distillation sequences with structure constraints, which can efficiently quantify and optimize the inherent safety index of each column configuration in the sequence, based on State-Task Network and Dow’s F&EI. To efficiently quantify the inherent safety index of each column configuration, a series of structure constraints are proposed. Within the superstructure, Hengstebeck-Underwood-Gilliland shortcut method is employed for distillation column design. Finally, two hazardous zeotropic mixture separation examples are performed to demonstrate the feasibility and validity of the proposed synthesis methodology.

Design of Atmospheric Petroleum Distillation Column

Design of Atmospheric Petroleum Distillation Column

Energy Integration and Reactive Distillation for Dimethyl Ether Synthesis via Catalytic Dehydration of Methanol

Distillation is the most widely used separation technique in the process industry. Its main disadvantage is the high consumption of thermal energy: the heat requirements of the distillation columns often represent most part of the total energy cost of the plant, appropriate integration of the distillation columns with the overall process often results in a significant reduction of the energy consumption in many cases.In this work the concept of the integration has been applied by two integrated design approaches:Heat-integrated design; where the distillation system of the process will be heat-integrated with the background process (i.e. integration between the distillation columns and the heat exchangers).Reactive distillation design; where the reaction and distillation will be accomplished in the same unit.The process of dimethyl ether (DME) synthesis by the catalytic dehydration of methanol has been considered as a case study. Heat-integrated design of DME process showed a significant total annual cost saving of 41 % compared to the conventional process, and the reactive DME distillation column design showed highest saving in total annual cost (TAC) by 81 %. In addition to the cost saving of the two proposed designs, also the flue gas emissions have been reduced using process integration methodology, where 51 % of the total emissions has been reduced by the heat-integrated design and 86 % by the reactive distillation column design.

Using the Method of Infinitely Sharp Splits for the Optimal Design of Extractive Distillation Units. 1. Ternary Mixtures

In this work, a novel sequential approach for optimal conceptual design of extractive distillation columns for the separation of ternary azeotropic mixtures was developed. This approach is based on...

Optimal design and dynamic transitions of multitask catalytic distillation columns: A Discrete-Steepest Descend Framework

This work presents the optimal design and operation of catalytic distillation (CD) units considering discrete and continuous design and operation variables combined with rigorous non-linear dynamic process models. The key novelty in this work is that optimal process design and dynamic transitions between different product grades in CD units are simultaneously intensified using a deterministic optimization framework. The proposed optimization method is based on a Discrete-Steepest Descent Algorithm (D-SDA), which enables the designer to improve an initial feasible design, while providing local optimality guarantees. The D-SDA has been effective to handle the optimal steady-state design of CD columns. The present study brings dynamic transitions into consideration thus providing theoretical foundations regarding the optimal design of CD columns in the transient domain. The production of ethyl tert-butyl-ether (ETBE) is considered as a case study, where dynamic transitions between different grades of ETBE coupled with design considerations are investigated. This work shows that a single CD unit can be optimally designed to produce multiple ETBE grades, while simultaneously optimizing its dynamic performance to attain different steady states. Accordingly, this study provides new insights regarding the economic and operational benefits of performing the simultaneous optimal design of multitask CD columns with dynamic transitions.