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Title:NAČRTOVANJE IN SINTEZA KEMIJSKIH PROCESOV Z UPORABO UČINKOVITIH MODELNIH TEHNIK IN REŠITVENIH STRATEGIJ
Authors:ID Ropotar, Marcel (Author)
ID Kravanja, Zdravko (Mentor) More about this mentor... New window
ID Novak-Pintarič, Zorka (Comentor)
Files:.pdf DR_Ropotar_Marcel_2009.pdf (2,36 MB)
MD5: BB919885D9BBE0CB0E8BDE86FE23D78B
PID: 20.500.12556/dkum/a7854d5e-e7e4-4606-a31d-241d3b699d6c
 
Language:Slovenian
Work type:Dissertation
Organization:FKKT - Faculty of Chemistry and Chemical Engineering
Abstract:V doktorski disertaciji obravnavamo modelne tehnike in strategije za reševanje sinteznih problemov, kjer nastanejo zapleteni modeli, ki so težko rešljivi. Modeli so kombinatorično zahtevni, nelinearni in/ali nekonveksni, zato se kljub že razvitim metodam in algoritmom pogosto pojavijo potrebe po novih, učinkovitejših strategijah in metodah. V prvem delu predstavljamo alternativno formulacijo konveksne lupine, ki temelji na mešano celoštevilski transformaciji spremenljivk. Transformacija spremenljivk transformira spremenljivke z ničelno spodnjo mejo v spremenljivke z ne-ničelno spodnjo mejo. Tako izvajamo optimiranje v ožjem preslikanem dopustnem prostoru lokalnih spremenljivk, to je spremenljivk, ki pripadajo alternativnim procesnim enotam. To nam pri reševanju mešano celoštevilskih linearnih in nelinearnih optimizacijskih primerov (MILP in MINLP) omogoča uporabo ne-ničelnih spodnjih mej. Z uporabo ne-ničelnih spodnjih mej se izognemo deljenju z nič in drugim matematičnim singularnostim. Pogosto pa so ne-ničelne spodnje meje uporabne, kadar imamo opravka s spremenljivkami, kot sta temperatura in pretok, ki morata imeti ne-ničelne vrednosti tudi kadar procesna enota ni izbrana. S transformacijo spremenljivk smo i) pretvorili konvencionalno formulacijo konveksne lupine v alternativno formulacijo in ii) konvencionalni algoritem zunanje poenostavitve spremenili v alternativni algoritem OA. Alternativno formulacijo konveksne lupine smo primerjali s formulacijo veliki-M in konvencionalno formulacijo na treh sinteznih primerih in izvedli več različnih eksperimentov. Rezultati kažejo, da je alternativna formulacija v večini primerov najbolj učinkovita glede računalniškega časa, števila iteracij in vozlišč. Ugotovili smo, da izbor vrednosti spremenljivk, ko alternativa ni izbrana, zelo vpliva na učinkovitost alternativne formulacije; in da je najprimernejša in najenostavnejša izbira kar spodnja ne-ničelna meja. Alternativno formulacijo in alternativni algoritem smo vnesli v procesni sintetizer MIPSYN in pri tem zmodelirali nove logične povezovalne člene in sprogramirali nov preprocesor za zunanje poenostavitve. Pogosto je dolg čas reševanja procesnih sinteznih problemov posledica zapletenih modelov reaktorjev. Zato smo za reaktorje, ki so opisani z diferencialnimi enačbami (šaržni, cevni) in jih rešujemo z metodo ortogonalne kolokacije končnih elementov, predlagali učinkovito numerično proceduro za reševanje. V sklopu procedure smo razvili model za dinamično optimiranje šaržnega reaktorja in preizkušali različne strategije in sheme, s katerimi smo povečevali robustnost modela. Nazadnje smo razvili še model za načrtovanje fleksibilnega šaržnega reaktorja, s katerim je mogoče tolerirati odstopanja procesnih parametrov. Pri reševanju motivacijskega primera šaržnega reaktorja se je kot najučinkovitejši izkazal model NLP s pomičnimi končnimi elementi. Ta model smo nato uporabili tudi za modeliranje niza elementov v cevnem reaktorju in izvedli sintezo MINLP študijske procesne sheme za proizvodnjo alilklorida ter z eno-parametričnim optimiranjem iz najboljših rešitev določili še ekonomsko območje. S predlagano alternativno formulacijo, novimi strategijami in robustnimi modeli za optimiranje reaktorjev je mogoče lažje reševati zapletene sintezne probleme, procesni sintetizer MIPSYN pa je tako postal še učinkovitejše programsko orodje za sintezo procesov in reševanje drugih tehniških problemov.
Keywords:procesna sinteza, procesni sintetizer, konveksna lupina, transformacija spremenljivk, splošno disjunktno programiranje, zunanje poenostavite, NLP, MINLP, šaržni reaktor, cevni reaktor, ortogonalna kolokacija, diferencialno-algebrski sistem enačb
Place of publishing:Maribor
Publisher:[M. Ropotar]
Year of publishing:2009
PID:20.500.12556/DKUM-10984 New window
UDC:66.061:519.852(043.3)
COBISS.SI-ID:246362112 New window
NUK URN:URN:SI:UM:DK:TLJLZORC
Publication date in DKUM:02.12.2009
Views:3771
Downloads:344
Metadata:XML DC-XML DC-RDF
Categories:KTFMB - FKKT
:
ROPOTAR, Marcel, 2009, NAČRTOVANJE IN SINTEZA KEMIJSKIH PROCESOV Z UPORABO UČINKOVITIH MODELNIH TEHNIK IN REŠITVENIH STRATEGIJ [online]. Doctoral dissertation. Maribor : M. Ropotar. [Accessed 31 March 2025]. Retrieved from: https://dk.um.si/IzpisGradiva.php?lang=eng&id=10984
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Secondary language

Language:English
Title:DESIGN AND SYNTHESIS OF CHEMICAL PROCESSES USING EFFICIENT MODELING TECHNIQUES AND SOLUTION STRATEGIES
Abstract:This PhD thesis deals with modelling techniques and strategies for solving synthesis problems, which give rise to complex models that are very difficult to solve, highly combinatorial, nonlinear, and/or non-convex. Therefore, more efficient strategies and methods have to be developed despite that several advanced methods, algorithms, and professional software tools already exist. In the first part of the PhD thesis, alternative convex hull formulation based on mixed-integer transformation is presented. Transformation of variables transforms zero-lower-bounded variables into nonzero-lower-bounded variables. Optimization is, thus, performed in narrowed lifted space of local variables (i.e. variables representing alternative process units). Therefore, variables with nonzero lower bounds can be used when solving mixed-integer linear (MILP) or nonlinear optimization (MINLP) problems. Using nonzero-lower-bounded variables division by zero and other mathematical singularities are avoided. Additionally, nonzero-lower-bounded variables are useful when variables cannot have non-zero values even when process unit is not selected (e.g. temperature and flow). Transformation of variables has been used for: i) transforming conventional convex hull into alternative convex hull and ii) transforming conventional OA algorithm into alternative one. Several studies were performed and three different large-scale synthesis problems were solved to compare the performance and efficiency of Big-M formulation, convex hull and alternative convex hull formulation. Preliminary results with the alternative convex hull representation indicate that the alternative convex hull representation is, in most cases, the most efficient with respect to the non-linear programming (NLP) and MILP steps. The results indicate that the selection of arbitrarily-forced values to which local variables are fixed when the corresponding alternatives are rejected is very important. An inappropriate selection of these values could severely decrease the efficiency of the MINLP search. Most likely the best and the most obvious choice for arbitrarily-forced value is lower bound. Alternative formulation and outer approximation algorithm were implemented in the process synthesizer MIPSYN and, additionally, new logical interconnection nodes have been modelled and new pre-processor for outer approximation was programmed. Longer solution times of process synthesis problems are often a result of complicated reactor models. Therefore, efficient numerical procedure for solving reactor problems with orthogonal collocation was proposed. Within the procedure, the model for dynamic optimization of a batch reactor was developed and, additionally, different schemes and strategies utilized in order to increase the model’s robustness. Finally, a batch reactor model for the design under uncertainty was developed. In the case of the motivating example of a batch reactor, the most efficient model was the one with moving finite elements. This model was then used to model the train of reactor elements in the plug flow reactor, and MINLP synthesis of allyl chloride production was performed. Additionally, the economic region was obtained by the one-parametric optimization. Using the proposed alternative formulation, new strategies and robust models for optimization of reactors, solving complicated synthesis models is now possible; moreover, process synthesizer MIPSYN was efficiently upgraded to solve process synthesis and other engineering problems.
Keywords:process synthesis, process synthesizer, convex hull, transformation of variables, generalized disjunctive programming, outer-approximations, NLP, MINLP, batch reactor, PFR reactor, orthogonal collocation, differential-algebraic system of equations


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