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Title:MINLP SINTEZA VODNIH OMREŽIJ IN OMREŽIJ TOPLOTNIH PRENOSNIKOV
Authors:Bogataj, Miloš (Author)
Kravanja, Zdravko (Mentor) More about this mentor... New window
Glavič, Peter (Co-mentor)
Files:.pdf DR_Bogataj_Milos_2010.pdf (15,93 MB)
 
Language:Slovenian
Work type:Dissertation (m)
Organization:FKKT - Faculty of Chemistry and Chemical Engineering
Abstract:V doktorski disertaciji obravnavamo dve tematiki s področja sinteze procesov. Prva je sinteza toplotno integriranih vodnih omrežij. Vodna omrežja so v takšni ali drugačni obliki integralni del praktično vseh kemijskih procesov. Zaradi relativno nizkih cen vode, nezavedanja o omejenosti vodnih virov in ohlapne okoljske zakonodaje so bila pogosto deležna premajhne pozornosti. Poleg same porabe vode in problematike, ki jo prinese njeno onesnaževanje z vrsto različnih onesnaževal, je enako problematična tudi spremljajoča poraba energije. V preteklosti se je izkazalo, da so rešitve sinteznih problemov, kadar obravnavamo snovne in energijske bilance ter investicijska sredstva in obratovalne stroške hkrati, v večini primerov boljše od tistih, ki jih dobimo na osnovi sekvenčnega pristopa. Iz tega razloga predlagamo simultan pristop k reševanju problematike toplotno integriranih vodnih omrežij. Sintezni problem zapišemo na osnovi matematičnega zapisa dveh med seboj povezanih superstruktur v obliki mešano celoštevilskega nelinearnega problema (MINLP). Prva je superstruktura vodnega omrežja, kjer so procesne enote med seboj povezane s tokovnicami preko mešalnikov in razdelivcev tokov. Druga je nadgrajena stopenjska superstruktura omrežja toplotnih prenosnikov, v kateri je omogočeno mešanje procesnih tokov. Predlagani pristop omogoča sintezo toplotno integriranih vodnih omrežij, v katerih je učinkovitost izrabe vode zasnovana na izkoriščanju možnosti njene ponovne uporabe in regeneracije. Energijsko učinkovitost dosegamo z izkoriščanjem posrednega prenosa toplote (v toplotnih prenosnikih) in neposrednega prenosa toplote (mešanje procesnih tokov). Strukture toplotno integriranih vodnih omrežij, ki jih dobimo z uporabo predlaganega pristopa, so topološko enostavne in ekonomsko učinkovite. Druga tematika je globalno optimiranje omrežij toplotnih prenosnikov. Ekonomsko ugodne rešitve problema sinteze omrežij toplotnih prenosnikov zagotovimo, kadar hkrati optimiramo investicijska sredstva, ki so vezana na ploščino toplotnih prenosnikov in obratovalne stroške, ki nastanejo zaradi porabe pogonskih sredstev. To zahteva formulacijo v obliki problema MINLP, ki je zaradi prisotnih nelinearnih funkcij nekonveksen. Posledično so dobljene rešitve lokalno optimalne. Za zagotavljanje globalne optimalnosti rešitev predlagamo formulacijo modela MINLP na osnovi stopenjske superstrukture in pridružene agregirane podstrukture, ki vsebuje število toplotnih prenosnikov in je blizu teoretičnega minimuma. Stopenjska superstruktura služi zgolj kot matrica za določanje termodinamsko dopustnih toplotnih stikov. Vse nekonveksnosti so prenesene v agregirano podstrukturo, kar močno zmanjša njihovo število. Konveksifikacijo nekonveksnih izrazov izvedemo z uporabo večnivojskih odsekovnih podcenitvenih funkcij, s katerimi zamenjamo vire nekonveksnosti. Konveksni model nato uporabimo za določevanje veljavne spodnje meje originalnemu nekonveksnemu problemu. Vrzel med veljavno spodnjo mejo in zgornjo mejo zmanjšamo do zadostitve tolerančnega kriterija z uporabo v ta namen razvitega večnivojskega algoritma, s katerim rešujemo konveksni problem MINLP.
Keywords:sinteza procesov, toplotno integrirana vodna omrežja, globalno optimiranje, omrežje toplotnih prenosnikov, mešano celoštevilsko nelinearno programiranje.
Year of publishing:2010
Publisher:M. Bogataj]
Source:[Maribor
UDC:66.042.88:621.565.93(043.3)
COBISS_ID:251660544 Link is opened in a new window
NUK URN:URN:SI:UM:DK:VIAJQDMB
Views:2622
Downloads:174
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Categories:KTFMB - FKKT
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Secondary language

Language:English
Title:MINLP SYNTHESIS OF WATER AND HEAT EXCHANGER NETWORKS
Abstract:This doctoral dissertation deals with two topics relevant to the field of process system engineering. The first one is synthesis of heat integrated water networks. Water networks are an integral component of practically each chemical process. They, however, often received little attention in a context of optimizing their water and energy efficiency. It was shown in the past that superior solutions to synthesis problems are expected to be obtained when material and energy balances as well as capital and operating costs are taken into account simultaneously. For this reason we propose a simultaneous optimization approach to solving problems of heat integrated water networks. The problem is formulated as a nonconvex mixed-integer nonlinear program (MINLP) based on the mathematical description of two intercombined superstructures. The first one is a superstructure of water network in which water using/regenerating units are interconnected with streams through sets of splitter and mixer units. The second one is an augmented stage-wise superstructure for heat exchanger network synthesis. The main feature of the latter is that mixing of streams is allowed within each stage. Thus, both indirect (via heat exchangers) and direct (via mixing of streams) heat exchange is taken rigorously into account. The heat integrated water network structures obtained using the proposed approach are simple in their topology and economically attractive. The second topic deals with global optimization of heat exchanger networks. The commonly accepted form of optimization model used in HEN synthesis problems corresponds to a nonconvex MINLP. Therefore, the obtained solution may not be unique. To guarantee global optimality of the solutions we propose a MINLP formulation based on a stage wise superstructure augmented by an aggregated substructure comprising a number of heat exchangers close to a theoretical minimum. The first one serves exclusively as a matrix for determening thermodynamically feasible matches among the streams, while the actual areas and corresponding costs of existing heat exchangers are determined in the latter. Through this a number of nonconvex terms is signifficantly reduced. The nonconvex terms are convexified by the use of piecewise multilevel underestimators. The convex MINLP model is then used to obtain a valid tight lower bound on the objective function of the original nonconvex model. The gap between the lower and upper bound is reduced to a predetermined tolerance by the use of the proposed multilevel algorithm.
Keywords:process synthesis, heat integrated water networks, global optimization, heat exchanger networks, mixed integer nonlinear programming.


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