Coupled Distillation Sequences Research Articles

Control of Thermally Coupled Distillation Arrangements with Dynamic Estimation of Load Disturbances

Because of their potential energy savings, thermally coupled distillation sequences provide interesting alternatives to the use of sequences based on conventional distillation columns. Three thermally coupled structures have been particularly analyzed for the separation of ternary mixtures: the sequence with a side rectifier, the sequence with a side stripper, and the Petlyuk column. Design methods have been developed for such sequences, but their dynamic and operational characteristics still require a wider understanding to promote their practical implementation. Previous works have shown that thermally coupled systems can provide suitable control properties; most of the studies on closed-loop control analysis of thermally coupled systems have been based on proportional−integral (PI) controllers. In this work, a PI controller with dynamic estimation of uncertainties is implemented for the control of the thermally coupled distillation arrangements. The controller comprises three feedback terms: proportional, integral, and quadratic actions. The last term provides a dynamic estimation of unknown load disturbances to improve the closed-loop performance. Comparison with the classical PI control law was carried out to analyze the performance of the proposed controller in facing unknown load disturbances in feed composition and set point changes. The results show that the implementation of the controller with dynamic estimation of uncertainties improved noticeably the closed-loop responses provided by the PI controller.

Controllability Analysis of Thermally Coupled Distillation Systems: Five-Component Mixtures

The theoretical control properties and dynamic responses under closed-loop operation of thermally coupled distillation sequences for the separation of five-component mixtures of hydrocarbons were c...

Control properties of thermally coupled distillation sequences for different operating conditions

The understanding of the dynamic behavior of distillation columns has received considerable attention due to the fact that distillation is one of the most widely used unit operations in chemical process industries. Thermally coupled distillation sequences (TCDS) can provide significant energy savings with respect to the operation of sequences based on conventional distillation columns. TCDS exhibit a complex structure, with recycle streams, that appear to affect their controllability properties. One potential solution to this problem has been suggested through the operation of TCDS under conditions that do not provide minimum energy consumption. The basic idea is that if one changes the operation point, the control properties might change as well. In this work, we analyze the dynamic behavior of two TCDS structures under different operating points, including the one with minimum energy consumption. The control analysis properties are analyzed with the application of the singular value decomposition technique at zero frequency and closed-loop dynamic responses using standard PI controllers. The results show that the controllability properties of distillation sequences may change significantly depending on the selected operation point.

Structural Considerations and Modeling in the Synthesis of Heat-Integrated−Thermally Coupled Distillation Sequences

This paper examines the design of mixed thermally coupled−heat-integrated distillation sequences. The approach considers a variety of methodologies, from conventional columns (each distillation column with a condenser and a reboiler) to fully thermally coupled systems (only one reboiler and one condenser in the entire system). A discussion about superstructure generation and the convenience of using a representation based on separation tasks instead of equipment is presented, as well as a set of logical rules in terms of boolean variables that allow all of the feasible structures to be generated systematically. Based on the logical rules, an algorithm is developed for generating valid sequences (even by hand) without explicitly solving the logical equations. All the specific aspects were related to intercolumn heat integration when partially thermally coupled systems are considered. A disjunctive programming formulation for extracting the optimal solution is presented. The model is based on the Fenske−Und...

Dynamic analysis of thermally coupled distillation sequences with undirectional flows for the separation of ternary mixtures

The Petlyuk distillation system has been considered with special interest because of the high energy savings it can provide with respect to the operation of sequences based on conventional columns. The original design of the Petlyuk structure, however, shows two interconnections that seem to affect its operational and controllability properties. To overcome this problem, two alternate structures have been suggested that use unidirectional flows of the vapor or liquid interconnecting streams. In this work, a comparative analysis of the control properties of the Petlyuk column and the alternate arrangements with unidirectional interconnecting flows is presented. Through a singular value decomposition analysis, it is shown that the alternate schemes provide better theoretical controllability properties than the Petlyuk system. Closed loop tests using proportional-integral controllers were also carried out, and the results showed that, in most of the cases considered, the alternate arrangements improved the dynamic responses of the Petlyuk column. Such arrangements, therefore, show promising perspectives for its practical consideration.

Design and Optimization of Thermally Coupled Distillation Schemes for the Separation of Multicomponent Mixtures

The design of thermally coupled distillation sequences for the separation of multicomponent mixtures is complex because of the greater number of degrees of freedom in comparison to distillation seq...

Thermodynamically equivalent distillation schemes to the Petlyuk column for ternary mixtures

Thermally coupled distillation sequences for ternary separations have been shown to provide significant energy savings with respect to the conventional direct and indirect distillation sequences. Although the Petlyuk column is generally more efficient than the other thermally coupled schemes, its structure creates potential operating problems because of the bi-directional vapour interconnecting streams. In this paper, second law calculations were performed for the Petlyuk column and six alternative distillation schemes that show unidirectional flows; in principle, such alternative configurations are expected to present better operational properties than those of the original Petlyuk column. The results indicate that the proposed distillation arrangements have values of thermodynamic efficiency very close to that of the Petlyuk column. This result is important because let us establish that the alternative distillation sequences: (i) are thermodynamically equivalent to the Petlyuk column, (ii) could be more easily implemented in practice, and (iii) also achieve significant energy savings.

Feedback Control Analysis of Thermally Coupled Distillation Sequences for Four-Component Mixtures

An analysis under closed loop operation of two thermally coupled distillation sequences for the separation of four-component mixtures was carried out and compared to the dynamic behaviour of a distillation sequence based on conventional columns. Responses to changes in set point for product compositions and to disturbances in feed compositions were obtained for operations with single closed loops and with four closed loops. The results indicate that the thermally coupled distillation systems are controllable, and that they may even show better dynamic responses than the conventional distillation sequence.

Effect of Recycle Streams on the Closed-Loop Dynamics of Thermally Coupled Distillation Sequences

ABSTRACT The effects of thermal links on the closed-loop dynamics of thermally coupled distillation sequences for the separation of quaternary mixtures have been studied in this work by using rigorous dynamic simulations. The incorporation of thermal links into conventional distillation sequences can lower the energy consumption up to 40% without introducing additional control problems to the resulting thermally coupled distillation sequences. In some cases, the thermally coupled distillation sequences outperformed the dynamic behavior of the conventional distillation sequences for set point tracking. This result is important to establish that thermally coupled distillation sequences not only can have significant energy savings but also good dynamic properties.

A Short Note on Control Structures for Thermally Coupled Distillation Sequences for Four-Component Mixtures

Thermally coupled distillation represents an alternative to conventional distillation to separate multicomponent mixtures. Industrial implementation of those systems can be achieved by using the divided-wall distillation column. It has been proven that a savings of up to 30% in the total annual costs can be obtained with these complex distillation sequences. In a previous work by Cardenas et al. (Cardenas, J. C.; Hernandez, S.; Gudino-Mares, I. R.; Esparza-Hernandez, F.; Irianda-Araraujo, C. Y.; Dominguez-Lira, L. M. Analysis of Control Properties of Thermally Coupled Distillation Sequences for Four-Component Mixtures. Ind. Eng. Chem. Res. 2005, 44, 391−399), it was found that thermally coupled distillation sequences not only can provide savings in the total annual costs but also can present good dynamic responses under closed-loop operation in contrast to distillation sequences based on conventional columns. In the previous study, pairings in the control loops were established according to practical cons...

Analysis of Control Properties of Thermally Coupled Distillation Sequences for Four-Component Mixtures

The control properties of thermally coupled distillation sequences for the separation of quaternary mixtures of hydrocarbons were compared to those of conventional distillation sequences. Two thermally coupled systems were investigated: a thermally coupled distillation sequence with side columns and a Petlyuk-type column. The preliminary steady-state design of the thermally coupled distillation sequences was obtained by starting from a conventional distillation sequence and then optimizing for minimum energy consumption. The control properties of the sequences considered were obtained by using the singular value decomposition technique and closed-loop dynamic simulations under feedback control. It was found that, for some frequencies, the thermally coupled distillation sequences present theoretical control properties similar to those of conventional distillation sequences, i.e., similar minimum singular values and condition numbers. Also, both types of distillation sequences show interactions when relative gain arrays were obtained. Then, when both types of distillation sequences were studied under the action of proportional integral controllers, the thermally coupled sequences also presented optimum dynamic responses similar to those obtained in the conventional distillation scheme. As a result, it can be concluded that thermally coupled distillation sequences can present theoretical control properties similar to those obtained in conventional distillation sequences. This result is significant because it lets one establish that the energy savings predicted for thermally coupled distillation sequences are achieved without introducing additional control problems.

Energy-Efficient Designs of Thermally Coupled Distillation Sequences for Four-Component Mixtures.

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTEnergy-Efficient Designs of Thermally Coupled Distillation Sequences for Four-Component Mixtures.Juan Luis Blancarte-Palacios, María Nancy Bautista-Valdés, Salvador Hernández, Vicente Rico-Ramírez, and Arturo JiménezCite this: Ind. Eng. Chem. Res. 2004, 43, 22, 7207–7208Publication Date (Web):September 25, 2004Publication History Published online25 September 2004Published inissue 1 October 2004https://doi.org/10.1021/ie0491387Copyright © 2004 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views196Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (59 KB) Get e-Alerts Get e-Alerts

Design of distillation sequences: from conventional to fully thermally coupled distillation systems

This work presents a novel superstructure optimization approach for the design of distillation sequences of zeotropic mixtures. The approach considers as alternatives from conventional sequences in which each final distillation column has a condenser and a reboiler, to fully thermally coupled distillation sequences going through all possible intermediate combinations. A two-stage procedure is proposed. In the first one, a sequence of tasks is selected and then in a second stage the best configuration of actual columns is extracted among all the thermodynamically equivalent configurations. The model uses the Underwood–Fenske–Gilliland approximation and is formulated as a generalized disjunctive programming problem. The model has proven to be very robust and reliable. This formulation also makes the model very flexible and allows the easy modification of the equations and even migration to other model types including rigorous tray-by-tray models. Rigorous simulations in HYSYS [AEA Technology, Hyprotech Ltd., Calgary, Canada, 2001] have shown good agreement with the shortcut model.

Thermodynamic Analysis of Thermally Coupled Distillation Sequences

Thermodynamic efficiency calculations have been performed for the separation of ternary and quaternary mixtures of hydrocarbons in both conventional and thermally coupled distillation sequences. When ternary mixtures were considered, energy savings achieved in the thermally coupled distillation sequences were between 10 and 30% in comparison to the two conventional distillation sequences. Regarding thermodynamic efficiency, thermally coupled distillation sequences presented the highest values in almost all of the cases considered. When the analysis was extended to the separation of quaternary mixtures, the thermally coupled distillation sequences show acceptable energy savings and the thermodynamic efficiency of a thermally coupled distillation sequence linked to a side stripper and a side rectifier was better than that obtained in the conventional distillation sequence; however, for the thermally coupled distillation with prefractionator (Petlyuk-type column), the second law efficiency was low when compared to that of the conventional distillation sequence for the separation of a quaternary mixture with a low content of intermediate components.

Energy Efficiency of an Indirect Thermally Coupled Distillation Sequence

AbstractSeveral thermally coupled distillation sequences have been proposed to improve the thermal inefficiency of conventional distillation sequences. Particularly, for the separation of ternary mixtures, structures that perform a lateral extraction in one of the columns of the integrated arrangement have been shown to provide significant energy savings. The structure of existing sequences, based on conventional distillation columns, might provide the basis for alternate thermally coupled designs. In this paper, it is shown how a thermally coupled system derived from an indirect conventional sequence can provide energy savings through a proper optimization of the interconnecting streams.

Energy-Efficient Designs of Thermally Coupled Distillation Sequences for Four-Component Mixtures

A design procedure for thermally coupled distillation sequences for the separation of four-component mixtures is presented. The schemes analyzed include a sequence with a side rectifier and a side stripper and a sequence with a prefractionator (Petlyuk-type column). Initial designs for the thermally coupled distillation sequences are obtained from the tray distribution of a conventional distillation sequence and then optimized for energy consumption using two interconnecting flows as search variables. Several tray arrangements for each thermally coupled design were analyzed, and the results show that the sequence with side columns can reach a lower energy consumption.

Control Behaviour of Thermally Coupled Distillation Sequences

The controllability properties of thermally coupled distillation sequences for the separation of ternary mixtures are compared with those of the conventional direct and indirect sequences. Closed loop responses to set point changes were performed, and controllers were tuned to minimize their ISE values. The results indicate that the integrated systems exhibit better control properties than sequences based on conventional distillation columns. This result provides a further incentive for the use of those integrated systems.

Sumitomo uses new metallocene catalyst in LDPE plant

Increasing the capacity of an existing distillation process has been a major focus of the chemical process industry. On the other hand, entrainment flooding can occur as a result, which can create a bottleneck in the distillation process. This paper reports the results of a techno-economic feasibility study to debottleneck the distillation column using a proposed hybrid process combining a heat pump and thermally coupled distillation sequence. Fractional utilization of the area was used to identify flooding problems in the column as well as how much area is available for vapor flow on an existing stage. A heat pump aided thermally coupled distillation sequence (HPTCDS) was designed and optimized using a response surface methodology. Two cases were examined to test the proposed sequence. The results showed that the proposed sequence can achieve significant energy savings and remove the bottleneck problem.

Analysis of Control Properties of Conventional and Nonconventional Distillation Sequences

In this paper a controllability analysis of seven distillation sequences for the separation of ternary mixtures using singular value decomposition and closed-loop responses under feedback control is presented. The results show that nonconventional distillation sequences such as thermally coupled distillation sequences can have better control properties than nonintegrated schemes, such as the conventional direct and indirect sequences, distillation systems with side streams, and sequences with three conventional distillation columns.

Controllability Analysis of Thermally Coupled Distillation Systems

A comparison of the controllability properties of three thermally coupled distillation sequences (Petlyuk, sequence with side rectifier, and sequence with side stripper) using singular value decomposition is developed. Those properties are also compared to the energy consumption required for separating ternary mixtures. The parameters obtained via singular value decomposition show that sequences with a side rectifier or a side stripper have better control properties than the Petlyuk system, although the Petlyuk scheme has lower energy requirements than the systems with side columns.