Petlyuk Column Research Articles

Energy Analysis and Remixing Effect of Thermal Coupling Petlyuk Column for Natural Gas Liquid (NGL) Fractionation Train

In this work, a non-conventional distillation sequence with thermal coupling (Petlyuk Column) was presented as a technique to perform the separation of the NGL consist of ethane, propane, butane or other higher alkanes. The improvements were investigated through the energy analysis and remixing effect. From the result obtained, it was found that the Petlyuk arrangement consumes less amount of energy and able to reduce the remixing effects as compared to the conventional column sequencing. The Petlyuk arrangement saved about 44.49% and 12.83% in terms of cooling and heating duty, respectively. The overall annual energy saving shown by this arrangement is 39.22%. This arrangement proved to be able to prevent the remixing effect occurrence that contributes to thermal and separation inefficiency. The desired separation efficiency also obtained by this arrangement as all the product specifications are met. The ability in avoiding remixing effect by the Petlyuk column permits a significant reduction in CO2 emission with an average of 29.43 % of each equipment involved. Hence, it can be concluded that the Petlyuk arrangement model is a better alternative to be implemented in the NGL fractionation train.

Second Law analysis of large-scale sugarcane-ethanol biorefineries with alternative distillation schemes: Bioenergy carbon capture scenario

Distillation is one of the most used separation techniques, despite its high heat demand and low thermodynamic efficiency. Although new distillation schemes have been developed for ethanol-water separation, most of them prescribe expensive sub-atmospheric columns. On the other hand, heat-integrated distillation columns allow significant steam savings since thermally integrated condenser/reboiler of different columns share the same heat duty. In this work, three innovative distillation schemes for large-scale sugarcane-ethanol biorefineries are analyzed aiming at less energy-intense processes, higher thermodynamic efficiencies and steam savings. Ethanol production, power production through bagasse-fired cogeneration, thermodynamic efficiency, heat demand, water usage, steam demand, carbon dioxide intake, and potential of bioenergy with carbon capture and storage are assessed for technical and thermodynamic comparisons of distillations schemes. Results of carbon emissions go beyond the biorefinery boundaries and include sugarcane supply-chain emissions. It is shown that heat-integrated distillation schemes promote huge steam savings compared to conventional ethanol distillation. Distillation Scheme No.2 – with five heat-integrated columns – showed highest steam savings of 63% relative to conventional distillation, while distillation Scheme No.3, prescribing an innovative Petlyuk column for bioethanol distillation, attained the highest thermodynamic efficiency (11.1%) outperforming distillation Schemes No.1 and No.2 (7.65% and 7.03%, respectively). Sankey diagrams express results of carbon dioxide equivalent flows, lost bioenergy with carbon capture and storage potential, water flow and equivalent power flows via the Second Law of Thermodynamics.

Eliminating the vapor split in dividing wall columns through controllable double liquid-only side-stream distillation configuration

The liquid-only transfer streams are sometimes preferred to replace the thermal coupling stream in distillation at similar energy efficiency for easier controllability. However, the dynamic controllability and practical control structures for such distillation configurations with liquid-only side-stream are still lacking. In search of a solution, this work investigates the dynamic performance of a double liquid-only side-stream process, which has the most complex structure but the lowest energy consumption among all possible liquid-only type ternary distillation configurations. With the aid of composition measurements, the control performances are generally well in case of adding feedforward controllers. Besides, the structure with only temperature controllers is also tested. On the occurrence of ±10% throughput and feed composition disturbances, the process is well-controlled with tiny product purity deviations. However, when the disturbances increase to ±20%, large offsets appear in some cases. To improve the effectiveness of the inferential control scheme, a modified structure with one internal composition controller is finally proposed to handle ±20% step changes. Overall, this work verifies well the easy controlling nature of the liquid transfer stream. The result of the work encourages the promotion of liquid-only side-stream configurations, as a competitive substitute of the well-known Petlyuk column or dividing wall column, for both academic and industrial purposes.

Experimental Studies of a Petlyuk Column and Validation of a Non‐Equilibrium Stage Model

AbstractIntegrated distillation equipment like the Petlyuk column offers enormous energy‐saving potential. However, high complexity and few available experimental data lead to high uncertainty. An integrated approach to reduce this risk is proposed. The first study on the influence of relative volatilities on the process behavior is presented. Comprehensive pilot‐plant experiments are displayed for three different component systems of linear alcohols. The experiments are carried out for a wide range of operating conditions. Results show a stable operation and high product purities. Based on the experimental data, a predictive non‐equilibrium stage model for column design is validated. Experiment and simulation indicate good agreement.

Controller Design and Sparse Measurement Selection in Self-optimizing control

Self-optimizing control focuses on minimizing loss for processes in the presence of disturbances by holding selected controlled variables at constant set-points. A measurement combination can be found, using the Null-space method, which further reduces the loss. Since self-optimizing control focuses on the steady-state operation, little attention has been put on the dynamic performance when selecting measurement combinations. In this work, an iterative LMI approach is combined with the sparsity promoting weighted l1-norm, to find a measurement subset together with PI controllers for the Null-space method. The measurement combination and the controllers are designed such that, the dynamic response is improved when the process is facing disturbances. The proposed method is illustrated on a Petlyuk column case study.

Synthesis of ternary distillation process structures featuring minimum utility cost using the IDEAS approach

A synthesis method for ternary distillation process structures is proposed on the basis of the infinite‐dimensional state‐space (IDEAS) approach. The proposed synthesis procedure consists of two steps. At the first step, the utility cost is minimized. The result of the first step contains many tiny flows among the modules because the number of flows is not included in the objective function. Then, at the second step, an evolutionary procedure for process simplification is executed. In this step, the weighted sum of flow rates is minimized recursively while updating the weights at each iteration. The practical process structure is finally determined from the result of the second simplification step. The developed synthesis procedure was applied to the separation problem of a ternary mixture consisting of benzene, toluene, and o‐xylene. It demonstrated that the proposed procedure provides a process whose liquid composition profile is quite similar to that of a Petlyuk column. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1285–1294, 2018

Control structure comparison for three-product Petlyuk column

Abstract The focus of this paper is to investigate different control structures (single-loop PI control) for a dividing wall (Petlyuk) column for separating ethanol, n-propanol and n-butanol. Four control structures are studied. All the results are simulations based on Aspen Plus. Control structure 1 (CS1) is stabilizing control structure with only temperature controllers. CS2, CS3 and CS4, containing also composition controllers, are introduced to reduce the steady state composition deviations. CS2 adds a distillate composition controller (CCDB) on top of CS1. CS3 is much more complicated with three temperature-composition cascade controllers and in addition a selector to the reboiler duty to control the maximum controller output of light impurity composition control in side stream and bottom impurity control in the prefractionator. CS4 adds another high selector to control the light impurity in the sidestream. Surprisingly, when considering the dynamic and even steady state performance of the proposed control structures, CS1 proves to be the best control structure to handle feed disturbances inserted into the three-product Petlyuk column.

Complex Systems of Distillation Columns Used in the Production of the Propylene Oxide

Complex systems of distillation columns were intensively studied within last decades and continue to show interest for researchers and for industrial application. The first designed complex distillation column with heat integration was the Petlyuk column and the development of complex systems of columns continued up to dividing wall columns (DWC) which are increasingly being used in industry. DWC are usually used to separate three products, components or fractions, from a multicomponent mixture. This study attempts to find the best fitting of complex systems of columns in the process of propylene oxide (PO) obtaining using the method of propylene chlorination and presents a proposed variant of separation which can lead to a reduced energy consumption. The fabrication of PO through this method lead to a multicomponent mixture which is separated in two main products: propylene oxide (PO) and heavier components containing as valuable compound 1,2 dichloropropane (DCP). Both products, PO and DCP, have important uses in the chemical industry. The study of complex schemes of columns used for PO separation was assessed by simulation using a simplified method based on Fenske � Underwood - Gilliland correlation (F.U.G.) [1]. The systems studied in this work include the following configurations of columns: column with prefractionator, column with partially coupled prefractionator, the Petlyuk column, the dividing wall column, column with side striper, column with side rectifier, the direct and the indirect sequence.

Petlyuk Columns in Multicomponent Distillation Trains: Effect of Their Location on the Separation of Hydrocarbon Mixtures

AbstractThermally coupled distillation columns (TCDC) are used to reduce energy requirements on the separation of liquid mixtures, which also reduces the environmental impact. The Petlyuk column is one of the TCDC with the highest reductions on heat duty. The use of distillation trains with Petlyuk columns is proposed to purify a multicomponent hydrocarbon mixture. Different sequences are studied, varying the location and number of Petlyuk columns to achieve separation of the components. Studied sequences are then optimized and compared in terms of energy requirements, environmental impact, and dynamic performance. The stream on which the component with the highest feed composition is separated has a great influence on the total heat duty and environmental impact. Nevertheless, the correlation between location and number of Petlyuk columns in the sequences and their control properties is low.

A new design method and operation of fully thermally coupled distillation column

From economic point of view, the fully thermally coupled distillation columns have shown benefits in terms of energy and capital cost savings when compared with conventional distillation columns. However, the design of such column systems is a topic of ongoing research because there are more degrees of freedom to deal with during the design phase. In this paper, a design method is presented and used to determine the structures of conventional two-product and Petlyuk columns, and the results show that the proposed design method works well. The steady state models are developed using HYSYS software, and the results show that the proposed design method provides good initial values for rigorous simulation. According to controllability analysis, the steady state models present better theoretical control properties; consistent with controllability results, when the steady state model is studied under closed-loop using PI controllers good dynamic responses for load rejection are obtained.

Distillation process optimization for styrene production from a styrene-benzene-toluene system in a Petlyuk column

The conventional way to produce styrene is ethyl-benzene dehydrogenation, which generates benzene and toluene as byproducts. In general, the separation of these three components is made through successive reactor product distillation, first removing benzene and, then, separating toluene from benzene. The main problem with the use of conventional distillation columns is excessive energy consumption in comparison with modern separation methods. This work simulates the conventional distillation system and the coupled column system (Petlyuk), in order to compare the benefits obtained on energy economy. The results show that, while the energy consumption to feed the boilers in the conventional distillation system is 2295kW, for the Petlyuk system the energy consumption was 1554kW, representing energy economy of 32.3%. Moreover, with application of this method higher purity was obtained for toluene, from 76.19% to 99.67%, and for styrene, from 99.71% to 99.98%.

Control System Design for Energy Efficient On-Target Product Purity Operation of a High-Purity Petlyuk Column

Energy efficient, on-target product purity operation of a high-purity three product benzene–toluene–xylene ternary Petlyuk column is studied. The basic regulatory control system consists of four temperature inferential control loops with a fixed prefractionator vapor-to-fresh feed ratio. An economic control system on top of the regulatory layer adjusts these five set points. It consists of three product purity controllers that adjust three temperature set points along with a reboiler duty reduction controller that adjusts the remaining two free set points in the regulatory layer. The latter makes these adjustments to prevent the downward curvature in the prefractionator and main column middle section temperature profiles from being too large. Closed loop results for large feed composition changes show significant energy savings (up to 15%) are realized via temperature profile curvature control compared to constant set point column operation. The case study highlights the need for innovative control strate...

Modified method to improve the design of Petlyuk distillation columns

BackgroundA response surface analysis was performed to study the effect of the composition and feeding thermal conditions of ternary mixtures on the number of theoretical stages and the energy consumption of Petlyuk columns. A modification of the pre-design algorithm was necessary for this purpose.ResultsThe modified algorithm provided feasible results in 100% of the studied cases, compared with only 8.89% for the current algorithm. The proposed algorithm allowed us to attain the desired separations, despite the type of mixture and the operating conditions in the feed stream, something that was not possible with the traditional pre-design method. The results showed that the type of mixture had great influence on the number of stages and on energy consumption. A higher number of stages and a lower consumption of energy were attained with mixtures rich in the light component, while higher energy consumption occurred when the mixture was rich in the heavy component.ConclusionsThe proposed strategy expands the search of an optimal design of Petlyuk columns within a feasible region, which allow us to find a feasible design that meets output specifications and low thermal loads.

Energy-Saving Mechanism in Heat Transfer Optimization of Dividing Wall Column

Currently most of the dividing wall column (DWC) designs are based on a Petlyuk Column in which the heat transfer process across the dividing wall is ignored. This paper proposes a heat transfer model of DWC, in which additional virtual intermediate heat exchangers are introduced between the prefractionator and the main column, and thus the heat transfer process among the virtual intermediate heat exchangers will produce the thermal-coupled effect. This effect can be explored by fixing the beneficial heat transfer region and a corresponding algorithm of heat transfer. Compared with the designs based on a Petlyuk Column, this DWC model can further reduce the exergy loss and energy consumption. Besides, the optimal operating zone is enlarged, and the influence of liquid and vapor split ratio fluctuation on the minimum energy consumption of DWC is lowered. This model provides a guidance for the energy-saving design of DWC.

Dynamic Simulation of Petlyuk Column for Separation of Ternary Mixtures

The Petlyuk distillation configuration has received considerable attention because of its efficiency to reduce the energy required for the separation of ternary mixtures. The dynamic properties of fully thermal coupling distillation column, which separates ternary mixtures of H2O, ethylene glycol (EG), diethylene glycol (DEG), are analyzed. The possible control configurations were investigated using Relative Gain Array (RGA) Analysis and dynamic simulation. The results indicate that the provided control scheme is able to produce a stable control response for thermally coupled distillation systems and shows better dynamic responses than the conventional distillation sequence.

Control structure selection for three-product Petlyuk (dividing-wall) column

This paper deals with selecting control structures for a three-product Petlyuk (dividing-wall) column with an objective to achieve desired product purities with minimum use of energy (V). We consider four alternate control structures with and without the vapor split as a degree of freedom. This work also demonstrates the usefulness of the graphical Vmin diagram to visualize minimum boilup requirement and choose the appropriate control structure.

Simplified Methodology for the Design and Optimization of Thermally Coupled Reactive Distillation Systems

New intensified schemes have been recently proposed as an attempt to reduce energy requirements and equipment costs in reaction–separation processes. A design methodology for thermally coupled reactive distillation systems is proposed in this work. To design the columns, a method based on the Fenske–Underwood–Gilliland (FUG) equations is proposed and tested. The FUG equations, the mass and energy balances, and the phase equilibrium equations are used to formulate the model of the intensified systems. Such a model is then solved as a nonlinear programming problem; the objective function is the minimization of the heat duty in the column. Biodiesel production through the esterification of oleic acid with supercritical methanol is used as a case study. Results show the feasibility of obtaining designs with low energy requirements by using the proposed methodology. Because of nonconvexities present in the formulation, the estimated interlinking flows for the reactive Petlyuk column might not correspond to a m...

Control structure selection for four-product Petlyuk column

Direct material coupling between column sections in distillation leads to energy efficient systems like the Petlyuk column but with more difficult control problems compared to conventional multicomponent distillation sequences. A control study of a four-product extended Petlyuk column operating close to minimum energy is reported here. We study the “ideal” case with all steady state degrees of freedom available for control, including the vapor split valves, which is required to achieve minimum energy under all conditions. Four decentralized control structures are proposed and tested against a wide range of disturbances. This work demonstrates also the use of the graphical Vmin tool which can be used to visualize the minimum boilup requirement for Petlyuk arrangements.

Divided wall distillation column: rationalization of degree of freedom analysis

The present work attempts to rationalize the degrees of freedom analysis of a divided wall distillation column for steady-state simulation using detailed mathematical model, which contains the MESHD equations (conventional MESH equation plus the pressure drop equation). In a divided wall distillation column, pressure difference plays an important role in deciding vapour and liquid flow rates across trays in the divided section. It is observed that for a given divided wall distillation column or Petlyuk column operating under steady state conditions with known feed and condenser pressure, the degrees of freedom is four. This is one higher than that for a conventional distillation column with three product streams (distillate, bottoms and the intermediate product). If this extra degrees of freedom is used to specify liquid split, then no extra degrees of freedom is left to specify vapour split ratio.

Optimal design of complex distillation system for multicomponent zeotropic separations

The optimal design of complex distillation system for separation of multicomponent zeotropic mixtures is studied. Super column with the ability to separate any specified products from the given feed is introduced for defining integration upper limit of design alternatives. The improved state-space (SS) superstructure incorporating all basic mass and heat transfer elements are adopted to capture all configurations in the framework of super column. Specifically, by adding stages-cascade process operator in the original representation, a series of optimal flowsheets with multiple thermal links, which have never been included within previous superstructure are easily generated. The mathematical modeling of the proposed superstructure is performed with mixed integer non-linear programming (MINLP). It advocates the use of rigorous physical model for each mass/heat transfer stage to ensure the practical reliability and optimality of the attained designs. Then the derived optimization model is solved by a modified solution procedure, in which the key item is an iterative initialization scheme. Three multicomponent zeotropic separation examples are employed to illustrate the effectiveness of the proposed approach. These optimum designs yield significant savings in total annual cost (TAC) relative to Petlyuk columns and some guidelines for distillation flowsheet retrofit based on thermodynamic analysis are proposed.