Synthesis of regional networks for biomass and biofuel production

doctoral dissertation

Hon Loong Lam (Author), Zdravko Kravanja (Mentor), Jiri Klemeš (Co-mentor)

Abstract

This thesis presents two different approaches to the synthesis of regional networks for biomass and biofuel production and supply: Mathematical Programming and Graph Theoretic approach. The optimisation criterion for both approaches is the maximisation of profit. The first approach is based on a generic optimisation model of biomass production and supply networks. This superstructure approach is based on a flexible number of network layers: plantation, collection using a pre-treatment, process, and consumption. A Mixed Integer Linear Programming (MILP) model has been successfully developed during this work. However, the solution of this biomass production network model is very challenging due to the large sizes of the networks and the number of interconnections. The huge number of redundant variables reduces model efficiency (time taken to solve the model and the interpretation of the results). This model when representing very large size networks cannot be solved over a reasonable time even by professional mathematical programming software tools. Several model-size reduction techniques are therefore proposedfor the solution of large-scale networks. In particular, methods are proposed for (i) reducing the connectivity within a biomass supply chain network by setting the maximum allowable distance between the supply zones to the collection centres, (ii) eliminating unnecessary variables and constrains to reduce the zero-flows in the full model, and (iii) aggregating the network and hence the synthesis process by merging the collection centres. The network synthesis is also carried out by P-graph (Process Graph) tools. P-graph is a directed bipartite graph, having two types of vertices - one for operating units and another for those objects representing material or energy flows/quantities. In this procedure, firstly a maximum feasible superstructure for biomass production network is generated from which the optimal structure is then selected by the Branch and Bound method. This graph-based method clearly shows where, how, and what kind of material and energy carriers will be transferred from one supply chain layer to another. In order to test the efficiency of the model, a small regional renewable network problem was solved using both methods. Their performances were tested and the results confirmed the applicability on a regional scale. The proposed model-size reduction techniques were also tested. A large-scale regional case study was created to demonstrate these techniques. The results are very positive and some suggestions for future work are given in the conclusion.

Keywords

mathematical programming;P-graph;MILP;

Data

Language:	English
Year of publishing:	2010
Source:	Maribor
Typology:	2.08 - Doctoral Dissertation
Organization:	UM FKKT - Faculty of Chemistry and Chemical Engineering
Publisher:	[H. L. Lam]
UDC:	66.011:519.68(043.3)
COBISS:	254123008
Views:	2998
Downloads:	101
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Other data

Secondary language:	Slovenian
Secondary title:	Sinteza regionalnih omrežij za proizvodnjo biomase in biogoriv
Secondary abstract:	V doktorski disertaciji predstavljamo dva različna pristopa k sintezi regionalnih omrežij za proizvodnjo in dobavo biomase in biogoriv: matematično programiranje in pristop, ki temelji na teoriji grafov. Uporabljen kriterij optimiranja pri uporabi obeh pristopov je maksimiranje dobička. Prvi, superstrukturni pristop temelji na splošnem optimizacijskem modelu omrežja za proizvodnjo in dobavo biomase in biogoriv. Pri tem superstrukturo sestavljajo štiri ravni dobavne verige: nivo proizvodnje obnovljivih surovin, nivo zbiranja s pred-obdelavo, nivo proizvodnje in nivo povpraševanja. S to raziskavo smo uspešno razvili mešano celoštevilski linearni programirni (MILP) model. Vendar pa predstavlja reševanje tega modela zaradi obsežnosti regionalnih omrežij z velikim številom povezav precejšen izziv. Veliko število odvečnih spremenljivk zmanjšuje učinkovitost reševanja (čas reševanja in razlago rezultatov). Obsežnih regionalnih omrežij tako pogosto ni mogoče rešiti v realnem času, četudi pri tem uporabljamo profesionalna matematično programirna računalniška orodja. Zato predlagamo nekatere tehnike za zmanjševanje velikosti mrežnih modelov. Predlagane tehnike so namenjene predvsem i) zmanjševanju števila povezav v omrežju z definiranjem največje dovoljene razdalje med dobavnimi conami in zbirnimi centri, ii) odpravi nepotrebnih ničelnih spremenljivk in pogojev in iii) zmanjšanju razvejanosti omrežja in s tem zmanjšanju sinteznega problema z združitvijo zbirnih centrov v manjše število centrov. Sintezo omrežja smo izvedli tudi z uporabo orodja P-graf ('procesni graf'). P-graf je usmerjeni dvopartitni graf z dvema vrstama oglišč - ena so za procesne enote in druga za objekte, ki predstavljaj osnovne ali energijske tokove oz. količine. V tem postopku se za omrežje proizvodnje in porabe biomase najprej generira maksimalna dopustna superstruktura, nakar se z metodo vejanja in omejevanja (Branch-and-Bound) izbere optimalna struktura. Pri tej metodi grafov je jasno razvidno, kako in kateri snovni in energijski nosilci se prenašajo iz enega na drugi nivo dobavne verige. Z namenom preizkušanja učinkovitosti modela smo najprej za regionalno omrežje rešili računsko manj zahteven problem in pri tem uporabili obe metodi ter preizkusili njuni zmogljivosti. Dobljeni rezultati potrjujejo uporabnost obeh metod za reševanje problemov na regionalni ravni. Preizkusili smo tudi učinkovitost predlaganih tehnik za zmanjšanje obsežnosti modela in zata namen razvili obsežnejši primer. Dobljeni rezultati so zelo obetavni. V zaključkih dodajamo tudi nekaj predlogov za nadaljnje delo.
Secondary keywords:	matematično programiranje;P-graf;MILP;
URN:	URN:SI:UM:
Type (COBISS):	Dissertation
Thesis comment:	Univ. Maribor, Fak. za kemijo in kemijsko tehnologijo
Pages:	XX, 144 str.
Keywords (UDC):	applied sciences;medicine;technology;uporabne znanosti;medicina;tehnika;chemical technology;chemical and related industries;kemijska tehnologija;kemijske in sorodne industrije;fundamentals of chemical engineering;osnove kemijskega inženirstva;mathematics;natural sciences;naravoslovne vede;matematika;mathematics;matematika;computational mathematics;numerical analysis;računska matematika;numerična analiza;
ID:	1013463