Analysis of Control Properties of Conventional and Nonconventional Distillation Sequences (original) (raw)
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Controllability Analysis of Thermally Coupled Distillation Sequences for Five – Component Mixtures
2015
The control properties of thermally coupled distillation sequences for the separation of five – component mixtures of hydrocarbons were compared to those of conventional distillation sequences. Seven thermally coupled arrangements were investigated. The preliminary steady – state designs of complex schemes were obtained by starting from conventional distillation sequences and then optimizing for minimum energy consumption. The control properties of the sequences considered were obtained by using the singular value decomposition technique at zero frequency and analyzing rigorous dynamic simulations. It was found that, in general, the coupled schemes present theoretical control properties similar or better than those of conventional distillation sequences. This result establishes that the energy savings predicted for thermally coupled distillation sequences can be achieved in practice. 1.
Industrial & Engineering Chemistry Research, 2005
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. †
2006
The thermally coupled distillation schemes have received considerable attention because of their efficiency to reduce the energy required for the separation of multicomponent mixtures. The structure of the complex systems offers some control challenges arising from the transfer of vapor (or liquid) streams between the columns. Recently, some alternate schemes to thermally coupled distillation arrangements for the separation of ternary mixtures, that might provide better operational properties than the complex columns, have been proposed. In this work, we analyze the control properties of two alternative distillation schemes to the coupled systems. The theoretical control properties have been analyzed with the application of the singular value decomposition technique. The results indicate that a reduction in the number of interconnections of the alternate configurations does not necessarily provide an improvement of their control properties.
Controllability Analysis of Thermally Coupled Distillation Systems: Five-Component Mixtures
Industrial & Engineering Chemistry Research, 2007
The control properties of thermally coupled distillation sequences for the separation of five-component mixtures of hydrocarbons were compared to those of conventional distillation sequences. Seven thermally coupled arrangements were investigated. The preliminary steady-state designs of complex schemes were obtained by starting from conventional distillation sequences and then optimizing for minimum energy consumption. The control properties of the sequences considered were obtained by using the singular value decomposition technique at zero frequency and analyzing rigorous dynamic simulations. It was found that, in general, the coupled schemes present theoretical control properties similar or better than those of conventional distillation sequences. This result establishes that the energy savings predicted for thermally coupled distillation sequences can be achieved in practice.
Feedback Control Analysis of Thermally Coupled Distillation Sequences for Four-Component Mixtures
Chemical Engineering Research and Design, 2005
A n 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.
Control properties of thermally coupled extractive distillation sequences
Proceedings of 5th International Symposium on Design Operation and Control of Chemical Processes, 2010
The structure of the thermally coupled distillation systems offers some control challenges arising from the transfer of vapor (or liquid) streams between the columns. In particular, the presence of recycle streams for coupled schemes has influenced the notion that control problems might be expected during the operation of those systems with respect to the rather well-known behavior of conventional distillation sequences. In this work, we analyze the control properties of thermally coupled extractive distillation schemes. The control properties are analyzed with the application of the singular value decomposition technique and a closed-loop analysis. The results showed that the energy savings predicted in the complex extractive distillation sequence can be achieved along with good dynamic behavior and reductions in greenhouse gas emissions.
Control Behaviour of Thermally Coupled Distillation Sequences
Chemical Engineering Research and Design, 2002
T he 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.
Computers & Chemical Engineering, 2008
Thermally coupled distillation systems (TCDS) have been proposed to perform distillation separation tasks with the incentive of achieving lower energy consumption levels with respect to conventional distillation sequences. In particular, the presence of recycle streams for TCDS schemes has influenced the notion that control problems might be expected during the operation of those systems with respect to the rather well-known behavior of conventional distillation sequences. That has been one of the main reasons for the lack of industrial implementation of thermally coupled distillation schemes. Recently, some alternatives to thermally coupled distillation arrangements that might provide better operational properties than the complex columns have been proposed. In this work, we analyze the control properties of two alternatives to the coupled systems. The results indicate that a reduction in the number of interconnections in alternate configurations does not necessarily provide an improvement of controllability properties.
Computer Aided Chemical Engineering, 2007
In this work we have extended the design and optimization methods for the separation of quaternary mixtures of hydrocarbons. Also, a controllability analysis using the singular value decomposition technique was performed in order to obtain the control properties of the distillation schemes. One conventional distillation sequence and three thermally coupled distillation sequences have been studied: one considering a side stripper and a side rectifier, one considering a side stripper and a side rectifier and heat integration between the side columns and a Petlyuk-type column. The design of a thermally coupled system starts from a conventional distillation sequence and then the recycle streams are varied until the minimum energy consumption is detected. The results show energy savings of around 30% of the thermally coupled distillation sequences in comparison to the conventional distillation sequence. Also, the system including both thermal and heat integration presented the lowest energy demand and the highest second law efficiency. When the integrated distillation sequences were subjected to a controllability analysis, the complex distillation sequence considering both thermal and heat integration presented the worst control properties in contrast to those of the complex schemes considering only thermal couplings.
Interaction and performance analysis of a ternary mixture distillation process
2019
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.