Integrated Process Design, Control and Analysis of Intensified Chemical Processes

Abstract

Procesdesign og processtyring er blevet betragtet som selvstændige problemer i mange år. I denne forbindelse anvendes en sekventiel tilgang, hvor processen er konstrueret først, efterfulgt af kontrol design. Men denne sekventielle tilgang har sine begrænsninger relateret til dynamiske constraint krænkelser, for eksempel tidsbegrænsninger arbejdspunkter, proces overdesign eller under-performance. Derfor, ved at bruge denne metode, en robust ydeevne er ikke altid garanteret. Desuden kan processen designbeslutninger påvirke processtyring og drift. For at overvinde disse begrænsninger, en alternativ metode er at tackle proces design og styrbarhed spørgsmål samtidigt, i de tidlige stadier af processen design. Denne samtidige syntese tilgang giver optimal / nær optimal drift og mere effektiv styring af konventionelle (ikke-reaktive binære destillationskolonner) samt komplekse kemiske processer; for eksempel intensiveret processer såsom reaktiv destillation. Vigtigst er det identificerer og fjerner potentielt lovende design alternativer, der kan have styrbarhed problemer senere. Til dato har en række metoder blevet foreslået og anvendt på forskellige problemer at løse samspillet mellem proces design og kontrol, og de spænder fra optimering tilgange til at modellere-baserede metoder. I dette afhandling, er integreret proces design og kontrol af reaktive destillation processer betragtes gennem en computerstøttet rammer. For at sikre, at beslutninger om design giver de optimale operationelle og økonomiske resultater, anvendelig og styrbarhed spørgsmål behandles samtidig med proces design spørgsmål. Operabilitet problemer løses for at sikre en stabil og pålidelig proces design på foruddefinerede driftsbetingelser mens styrbarhed anses for at opretholde ønskede arbejdspunkter i processen på pålagte forstyrrelser i foderet under normale driftsforhold. Først et sæt design metoder, der ligner i koncept til design af ikke-reaktive destillationer, såsom McCabe-Thiele og drivkraft tilgang valgt at designe den reaktive destillationskolonne. Dernæst er disse designmetoder udvides ved hjælp element koncept til også at omfatte ternære samt flerkomponent reaktive destillation processer. Elementet begrebet anvendes til at oversætte et ternært system med forbindelserne (A + B ↔ C) til et binært system af elementer (WA og WB). Når kun to elementer er nødvendige for at repræsentere den reagerende system med mere end to forbindelser, er et binært element system har identificeret. I tilfælde af multi-element reaktiv destillation processer (hvor mere end to elementer er stødt) den ækvivalente element begrebet anvendes til at oversætte en multikomponent (multi-element-system) i forbindelserne (A + B ↔ C + D) til et binært system af centrale elementer (elementer WHK og WLK). For et energieffektivt design, ikke-reaktivt drivkraft (for binær ikke-reaktivt destillation), reaktiv drivkraft (for ternære sammensatte reaktiv destillation) og binær-ækvivalent drivkraft (for flerkomponent reaktiv destillation) blev anvendt. For både McCabe-Thiele og drivkraft metode, er damp-væske ligevægt data baseret på elementer. Det har været påvist, at designe en reaktiv destillationskolonne ved maksimal drivkraft vil resultere i minimalt energiforbrug. Bemærk, at de samme principper, som gælder for en binær ikke-reaktiv forbindelse systemet gælder også for et binær-element eller et multi-element-system. Derfor er det fordelagtigt at anvende elementet metode til flerkomponent reaktion-separation.Det er vist, at de samme design-kontrol principper, der gælder for en ikke-reagerende binære system af forbindelser gælder også for et reaktivt binært system af grundstoffer eller multi-elementer til destillationskolonner. Anvendelsen af denne ramme viser, at designe den reaktive destillation ved de maksimale drivkraft resulterer i en gennemførlig og pålidelig udformning af processen samt controller struktur. Gennem analytiske, steady-state og lukket-sløjfe dynamisk analyse er det bekræftet, at kravet om kontrol struktur, forstyrrelse afvisning og energi af den reaktive destillationskolonne er bedre end nogen anden operation punkt der er slet ikke den maksimale drivkraft. Endvidere er det vist, at designet ved maksimal drivkraft kan både styres ved hjælp af simple regulatorer såsom PI samt avancerede regulatorer såsom MPC. Process design and process control have been considered as independent problems for many years. In this context, a sequential approach is used where the process is designed first, followed by the control design. However, this sequential approach has its limitations related to dynamic constraint violations, for example, infeasible operating points, process overdesign or under-performance. Therefore, by using this approach, a robust performance is not always guaranteed. Furthermore, process design decisions can influence process control and operation. To overcome these limitations, an alternative approach is to tackle process design and controllability issues simultaneously, in the early stages of process design. This simultaneous synthesis approach provides optimal/near optimal operation and more efficient control of conventional (non-reactive binary distillation columns) as well as complex chemical processes; for example, intensified processes such as reactive distillation. Most importantly, it identifies and eliminates potentially promising design alternatives that may have controllability problems later. To date, a number of methodologies have been proposed and applied on various problems to address the interactions between process design and control, and they range from optimization-based approaches to model-based methods. In this work, integrated process design and control of reactive distillation processes is considered through a computer-aided framework. To assure that design decisions give the optimum operational and economic performance, operability and controllability issues are considered simultaneously with the process design issues. Operability issues 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 imposed disturbances in the feed under normal operating conditions. First, a set design methods, similar in concept to design of non-reactive distillations, such as McCabe-Thiele and driving force approach are selected to design the reactive distillation column. Next, these design methods are extended using element concept to also include ternary as well as multicomponent reactive distillation processes. The element concept is used to translate a ternary system of compounds (A + B ↔ C) to a binary system of elements (WA and WB). When only two elements are needed to represent the reacting system of more than two compounds, a binary element system is identified. In the case of multi-element reactive distillation processes (where more than two elements are encountered) the equivalent element concept is used to translate a multicomponent (multi-element) system of compounds (A + B ↔ C + D) to a binary system of key elements (elements WHK and WLK). For an energy-efficient design, non-reactive driving force (for binary non-reactive distillation), reactive driving force (for binary element systems) and binary-equivalent driving force (for multicomponent reactive distillation) were employed. For both the McCabe-Thiele and driving force method, vapor-liquid equilibrium data are based on elements. It has been is demonstrated that designing a reactive distillation column at the maximum driving force will result in the minimum energy consumption. Note, that the same principles that apply to a binary non-reactive compound system are valid also for a binary-element or a multi-element system. Therefore, it is advantageous to employ the element based method for multicomponent reaction-separation systems. It is shown that the same design-control principles that apply to a non-reacting binary system of compounds are also valid for a reactive binary system of elements or multi-elements for distillation columns. Application of this framework shows that designing the reactive distillation process at the maximum driving force results in a feasible and reliable design of the process as well as the controller structure. Through analytical, steady-state and closed-loop dynamic analysis it is verified that the control structure, disturbance rejection and energy requirement of the reactive distillation column is better than any other operation point that is not at the maximum driving force. Furthermore, it is shown that the design at the maximum driving force can be both controlled using simple controllers such as PI as well as advanced controllers such as MPC