Student Number : 0314958W - MSc dissertation - School of Process and Materials Engineering - Faculty of Engineering and the Built Environment / Microstructural characterisation was performed on Al-Ti-B grain refiners of different compositions prepared by aluminothermic reduction of TiO2 and B2O3 and dilution of the products in aluminium melts. The microstructure of the grain refiners showed needle-like TiAl3 particles as well as prismatic TiB2 particles. The TiB2 particles were coarser than those in conventional Al-Ti- B grain refiners. The microstructure also showed silicon particles and, in some cases, titanium carbide particles (TiC). The experimental grain refiners were subjected to rolling and reduced in thickness by 20, 40, 60 and 80%. The rolled samples were then heated at 625°C for 4 hours and allowed to cool slowly in the furnace. Significant changes in microstructure were noticed at 80% reduction. The flake-like and needle-like aluminide particles in the as cast microstructure were fragmented and aligned in the aluminium matrix, giving rise to short needle-like particles in parallel rows. These aluminide particles had rough edges which were rounded by heat treatment. The TiB2 particles were not affected in size or morphology by either the rolling or the heat treatment. The grain refining performance of the as cast materials was assessed. It was found that the experimental grain refiners had poorer performance than commercial grain refiners. The influence of mechanical and thermal treatments on the grain refining performance of the experimental Al-Ti-B grain refiners was also assessed. Cold working of the grain refiners had a positive influence on the grain refining performance promoting finer grain. Heat treatment of grain refiners after cold working was deleterious and led to a loss of grain refining capacity. The size and size distribution of TiB2 particles were determined related to grain refining performance and compared to theoretical models. A relationship was established between the size distribution of the TiB2 particles in the grain refiners and the grain size of inoculated aluminium. Grain refinement increased with decreasing proportion of coarse TiB2 particles in the grain refiners. This corresponded to a decrease in Ti and B contents and an increase in the Ti/B ratio.

Some oil refining companies have recently entered the field of exploration and production (E&P). Both the relatively high financial performances of E&P companies and the shrinking refining margin may motivate refiner’s decision to enter E&P. However, in making this decision, there are other factors to be considered. This study utilizes vertical integration and diversification theories to develop an integrated framework. This framework determines the factors which should be involved in a firm’s decision to enter another business area. In this theoretical approach and its application to Korean refining companies’ decision to enter into E&P, we discuss both the cost benefits and the advantages to acquiring strategic assets of the new business. As sources of short-term cost benefits, the paper discusses site specificity and regional performance. As long-term requirements, the paper explores the need to acquire E&P strategic assets. In early-stage decision making, the best mode may be a small equity investment in regional consortia. As a company acquires more and more strategic assets, it can decide to pursue global opportunities and/or to acquire an E&P company. / text

Ο πρωταρχικός στόχος αυτής της εργασίας είναι να μελετηθεί η υποδιαδικασία κατά την παραγωγή χαρτιού, γνώστη και ως πολτοποίηση. Η πολτοποίηση αφορά το στάδιο οπού το πριονίδι, παρουσία νερού περνά μέσα από τον πολτοποιητή ο οποίος αποτελείται από δύο πιάτα που περιστρέφονται με αντίθετη φορά, το πριονίδι διαλύεται και μαζί με το νερό δημιουργούν το μίγμα του χαρτοπολτού. Η εν λόγω διαδικασία χαρακτηρίζεται από υψηλή πολυπλοκότητα λόγω της δυσκολίας που παρουσιάζει στη μαθηματική μοντελοποίηση. Σε αυτή την εργασία, εξετάζονται ήδη υπάρχουσες προσεγγίσεις στο θέμα της μοντελοποίησης. Διαφορετικές προσεγγίσεις πάνω στη μοντελοποίηση εχουν γίνει τα τελευταία χρόνια από τους μηχανικούς, υπό την έννοια οτι χρησιμοποιήθηκαν διαφορετικές μεταβλητές ως έξοδοι και ως είσοδοι και πληθώρα μεθόδων μοντελοποίησης. Τα σημαντικότερα μοντέλα ανοιχτού βρόχου που βρεθήκαν στη βιβλιογραφία εξομοιώνονται και τα χαρακτηριστικά τους αναλύονται. Ο στόχος της εργασίας είναι να καθοριστεί αν οι προαναφερθείσες μοντελοποιήσεις μπορούν να ελεγχθούν με επιτυχία μέσω ενός Model Predictive Controller (MPC). Εκτεταμένες προσομοιώσεις πραγματοποιούνται όπου οι παράμετροι του ελεγκτή εξετάζονται λεπτομέρως ώστε να διαπιστωθεί το αντίκτυπο τους στην όλη διαδικασία. Προκειμένου να εξεταστεί η αποδοτικότητα του ελεγκτή, δεδομένα τα οποία πάρθηκαν από πραγματική βιομηχανία συγκρίνονται με αυτά του MPC τα οποία παράχθηκαν μέσω του MATLAB. / The initial objective of this diploma thesis is to investigate and examine the papermaking’s sub-process also known as pulping. Pulping concerns the stage where wood chip along with water is being passed through a refiner that consists of two counter rotating discs, woodchip is being smashed and with the presence of water the pulp mixture is being created. This process is being characterized as highly complex because of the difficulties that appear in its mathematical modeling. In this thesis, the existing modeling approaches developed for the pulp and paper refining process are also being investigated. Different approaches have been developed towards the modeling of the process during the past years, where engineers utilized different controlled and manipulated variables as well as a variety of modeling methods. The most important pulp and paper refiner open-loop model approximations, extracted from the existing related literature, are being simulated and their characteristics are being examined in detail. This work’s main and final objective is to determine if the aforementioned modeling approaches of the pulp and paper refining process can be successfully controlled via a Model Predictive Control (MPC) based structure. Extensive simulation trials are being carried out, where the MPC parameters are being investigated in detail regarding their effect on the overall control performance of the pulp and paper refining process. In order to further evaluate the efficacy of the proposed control scheme, the MPC related results are being compared to experimental data extracted from a real refining system that utilizes a generic industrial controller.

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Thesis (MBA)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Changes in the global salt market have presented Walvis Bay Salt Refiners with an opportunity to increase its current sales by approximately 40%. Following several pre-feasibility studies, the expansion project plan was created. The construction of new ponds, canals and sluices were to be performed by a subcontractor as selected through a tender process. The scope of the work comprised approximately 70% of the total project cost and it also represented the most critical part of the expansion project. Thomas Saaty’s Analytic Hierarchy Process, was used as a group decision support system for the selection of the most suitable subcontractor. The weighted average mean method was used to aggregate individual scores. A sensitivity analysis was performed following the final outcome to gain a deeper understanding of the problem, obtain a measure of margin between subcontractor scores and to check for the correctness of numbers. / AFRIKAANSE OPSOMMING: Veranderinge in die wêreld soutmark het vir Walvis Bay Salt Refiners 'n geleentheid gebied om sy verkope met ʼn beraamde 40% te verhoog. Na verskeie voorondersoeke is 'n volledige projekplan opgestel. Die vervaardiging van damwalle, kanale en sluise sou deur 'n kontrakteur gedoen word wat deur ʼn tenderprosedure gekeur sou word. Die omvang van hierdie gedeelte van die uitbreidingsprojek verteenwoordig ongeveer 70% van die totale projekkostes en is terselfdelyk die mees sensitiewe gedeelte van die projek. Thomas Saaty se Analytic Hierarchy Process is gebruik as die groepbesluitnemingsondersteuningstelsel om die mees geskikte kontrakteur te kies. Die geweegde gemiddelde is gebruik om die individuele oordele saam te voeg. Sensitiwiteits analise is uitgevoer nadat die finale uitslag bepaal is om sodoende beter insig in die probleem te ontwikkel, om ʼn beter onderskeiding tussen die kontrakteur puntetellings te kry en om die juistheid van die syfers na te gaan.

The main objective of this thesis was to improve the understanding of some aspects on wood and fibre mechanics related to conditions in the thermomechanical pulping process. Another objective was to measure the power distribution between the rotating plates in a refiner.   The thesis comprises the following parts: –A literature review aimed at describing fracture in wood and fibres as related to the thermomechanical pulping process –An experimental study of fracture in wood under compression, at conditions similar to those in feeding of chips into preheaters and chip refiners –An experimental study of the effect of impact velocity on the fracture of wood, related to conditions of fibre separation in the breaker bar zone in a chip refiner –A micromechanical model of the deterioration of wood fibres, related to the development of fibre properties during the intense treatment in the small gap in the refining zone –Measurements of the power distribution in a refiner.   The fracture in wood under compression was investigated by use of acoustic emission monitoring. The wood was compressed in both lateral and longitudinal directions to predict preferred modes of deformation in order to achieve desired irreversible changes in the wood structure. It was concluded that the most efficient compression direction in this respect is longitudinal. Preferable temperature at which the compression should be carried out and specific energy input needed in order to achieve substantial changes in the wood structure were also given.   The fibre separation step and specifically the effect of impact velocity on the fracture energy were studied by use of a falling weight impact tester. The fracture surfaces were also examined under a microscope. An increase in impact velocity resulted in an increase in fracture energy. In the thermomechanical pulping process the fibres are subjected to lateral compression, tension and shear which causes the creation of microcracks in the fibre wall. This damage reduces the fibre wall stiffness. A simplified analytical model is presented for the prediction of the stiffness degradation due to the damage state in a wood fibre, loaded in uni-axial tension or shear. The model was based on an assumed displacement field together with the minimum total potential energy theorem. For the damage development an energy criterion was employed. The model was applied to calculate the relevant stiffness coefficients as a function of the damage state. The energy consumption in order to achieve a certain damage state in a softwood fibre by uniaxial tension or shear load was also calculated. The energy consumption was found to be dependent on the microfibril angle in the middle secondary wall, the loading case, the thicknesses of the fibre cell wall layers, and conditions such as moisture content and temperature. At conditions, prevailing at the entrance of the gap between the plates in a refiner and at relative high damage states, more energy was needed to create cracks at higher microfibril angles. The energy consumption was lower for earlywood compared to latewood fibres. For low microfibril angles, the energy consumption was lower for loading in shear compared to tension for both earlywood and latewood fibres. Material parameters, such as initial damage state and specific fracture energy, were determined by fitting of input parameters to experimental data. Only a part of the electrical energy demand in the thermomechanical pulping process is considered to be effective in fibre separation and developing fibre properties. Therefore it is important to improve the understanding of how this energy is distributed along the refining zone. Investigations have been carried out in a laboratory single-disc refiner. It was found that a new developed force sensor is an effective way of measuring the power distribution within the refining zone. The collected data show that the tangential force per area and consequently also the power per unit area increased with radial position. The results in this thesis improve the understanding of the influence of some process parameters in thermomechanical pulping related wood and fibre mechanics such as loading rate, loading direction, moisture content and temperature to separate the fibres from the wood and to achieve desired irreversible changes in the fibre structure. Further, the thesis gives an insight of the spatial energy distribution in a refiner during thermomechanical pulping.