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For a binary element system, a simple reactive McCabe-Thiele-type method ... reactive McCabe-Thiele and driving force method, vapor-liquid equilibrium data ...
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Maria-Ona Bertran, Thomas Bisgaard and Rebecca Frauzem (Eds.), 12th International Symposium on Process Systems Engineering and 25th European Symposium on Computer Aided Process Engineering. 31 May - 4 June 2015, Copenhagen, Denmark © 2015. All rights reserved.

Track 5. Process Dynamics, Control and Monitoring

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A New Software Development Methodology for Controllability Analysis of Forced Circulation Evaporator System

A Model-Based Methodology for Integrated Design and Operation of Reactive Distillation Processes

Afshin Sadrieh *, Parisa A. Bahri

Seyed Soheil Mansouri a,*, Mauricio Sales-Cruz b, Jakob K. Huusom a, John M. Woodley a, Rafiqul Gani a

School of Engineering and Information Technology, Murdoch University, 90 South Street, Perth 6150, Australia

a

Modern processing plants are becoming more and more complex due to the tighter economical and environmental limitations. As a result, unit operations become more coupled and more non-linear. The more dependent and non-linear the unit operations, the harder it is to maintain the process outputs within the feasible and optimal operating regime. The ability to handle the process system outputs by using feedback control is called controllability of process design. Studies show that poor controllability of a plant can result in long-term economicdrawbacks and safety hazards. There are many controllability assessment methods available in the literature. These methods are divided into two main groups: linear and non-linear measurements. Dynamic resilience, as a linear measurement, is defined as the quality of the regulatory and servo behaviour which can be obtained by feedback control (Garcia and Morari, 1982). On the other hand, controllability of a process is inherited directly from the design itself (Yuan et. al, 2010), which means that regardless of the controller and controlling strategy, the controllability index is constant. Therefore, evaluation process of the plant-wide design, from controllability point of view should be takenintoconsideration at the design stage. Despite the need for software tools for controllability assessment at the earlier stage of process design, there is no world class software tool available in this field. Our studies suggested that is it due to two major reasons: firstly, it is because of the problem-specific nature of the controllability problems. Almost in every case, a unique method ofmeasurement is used for controllabilityassessment. This means that for every controllability problem there should be a unique software developed, which makes it economically unbeneficial for the software companies to enter this domain; and secondly, because of the interdisciplinarycharacteristics of the controllability problems, a group of expertise from different fields, such as chemical, control and software engineering, with acceptable level of knowledge of the problem should be assembled, which makes the process of software development even harder and more expensive. In this work a graphical domain-specific language (DSL) is introduced for measuring RGA index, to assess the controllability of a process system. DSL is a computer programming language of limited expressiveness focused on a particular domain (Fowler, 2012). In other words, DSL brings new technologies of developing programming languages together, so the development cost drops dramatically. This programming language uses symbols and notations, which are well known by the domain experts, i.e. process engineers. Therefore, it addresses the communication problem between programmers and process engineers. In this work, DSL is applied to a non-linear evaporator system.The process consists of an evaporator, separator, condenser and a recycling pump. The goal in this system is to control the concentration of the outlet stream, the evaporator pressureand the liquid level in the separator by manipulating the pressure of theinlet steam, the coolant flowrate and the outlet flow-rate. The proposed programming language is shown to be capable of analysing the process system design and reporting the RGA index. Also, the controlled uncertainties are applied on the input variables and their impact on the controllability index is discussed.Finally the advantages of using the proposed DSL methodology over the conventional models are presented.

CAPEC-PROCESS, Department of Chemical and Biochemical Engineering, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark Departamento de Procesos y Tecnología, Universidad Autónoma Metropolitana-Cuajimalpa, 05300, Mexico

b

Process intensification is a new approach that has the potential to improve existing processes as well as new designs of processes to achieve more profitable and sustainable production. However, many issues with respect to their implementation and operation is not clear; for example, the question of operability and controllability. Traditionally process design and process control are considered as independent problems and are solved sequentially. The process design problem is usually solved to achieve the design objectives, and then, the operability and process control issues are identified, analyzed and resolved. A new approach is to tackle process intensification and controllability issues in an integrated manner, in the early stages of process design. This integrated and simultaneous synthesis approach provides optimal operation and more efficient control of complex intensified systems that suffice the process design objectives. Furthermore, it may also suggest innovative process alternatives which are more economical and environmental sustainable. In this work, a systematic model-based methodology for integrated design and operation of reactive distillation operations is presented. Issues related to operation are addressed to ensure a stable and reliable process design at pre-defined operational conditions whereas controllability is considered to maintain desired operating points of the process at any kind of imposed disturbance under normal operating conditions. The methodology employs a decomposition-based method so that the complexity of the problem is reduced into a set of sub-problems that are solved sequentially. The method consists of four hierarchical stages: (1) pre-analysis, (2) steady state analysis, (3) dynamic analysis, and (4) evaluation stage. To illustrate the application of the proposed methodology, production of methyl-tert-butyl-ether (MTBE) using a reactive distillation column (RDC) is considered. Simple graphical design methods that are similar in concept to non-reactive distillation processes are used. The methods are based on the element concept, which is used to translate a ternary system of compounds (methanol, isobutene and MTBE) to a binary system of elements (elements A and B). For a binary element system, a simple reactive McCabe-Thiele-type method (to determine the number of reactive stages) has been used. The reactive equilibrium curve is constructed through sequential calculation of reactive bubble points. For an energy-efficient design, the driving-force approach (to determine the optimal feed location) for a reactive system has been employed. For both the reactive McCabe-Thiele and driving force method, vapor-liquid equilibrium data are based on elements. The reactive bubble point algorithm is used to compute the reactive vapor-liquid equilibrium data set. The operation of the RDC at the highest driving force and other candidate points is compared through openloop and closed-loop analysis. By application of this methodology it is shown that designing the process at the maximum driving force results in an energy efficient and operable design. It is verified that the reactive distillation design option is less sensitive to the disturbances in the feed at the highest driving force and has the inherent ability to reject disturbances.

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