Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Thermodynamic models have been investigated extensively since Johannes van der Waals first devised a mathematical relation capable of predicting both vapour and liquid phases for a mixture at equilibrium. With the advent of modern computing power, these equations of state have gone from their humble empirical beginnings to the comprehensive and fundamentally derived models we have today. One such physically sound model is the Statistical Associating Fluid Theory (SAFT) family of equations, derived from the molecular perturbation theories of the 1980’s. The relative youth of this thermodynamic framework has meant that much work has gone into modification and optimisation of the model recently. The variants of particular interest to this work are the simplified perturbed chain SAFT equations with the Jog & Chapman (sPC-SAFTJC) and Gross & Vrabec (sPC-SAFTGV) polar terms. Each of the polar terms supports one adjustable polar parameter that relates to the quantity of polar segments in the reference fluid but not necessarily its position in the carbon chain. The strength of polar interactions is known to decrease as the functional group moves away from the terminal methyl group and the effects of steric hindrance increase. Thus, in question here is whether the models can account for the change in polar interactions associated with the changing position of the polar group, by only adjusting the values of the existing pure component parameters; that is, in lieu of a position specific parameter. The carbonyl group in ketone molecules is one such polar group, and it is this homologous series that is the focus of this study. The decrease in polar interactions as the carbonyl group in a ketone molecule shifts centrally is apparent from the lower boiling points of the isomers where the polar group is central as compared to those where the functional group is nearer the terminal methyl group. The effect of this functional group shift on binary phase behaviour has not previously been assessed for any system however, as the lack of experimental data attests. Thus, experiments had to be conducted to generate phase equilibrium data for systems comprising each structural isomer of a mid-length ketone with a common second component with no functionality. This limitation was imposed to isolate the cause of experimentally observed phenomena to the shifting polar group alone. The generated data could then be appropriately modelled using the polar sPC-SAFT variants and the capabilities of each model, as outlined above, assessed. To this end, isobaric binary vapour-liquid equilibrium data were measured for 2-, 3- & 4-heptanone with three separate normal alkanes of similar length (n-octane, n-nonane & n-decane) at 40kPa. The apparatus used was a dynamic Gillespie VLE still with temperature and pressure accuracies of 0.03°C and 1.6mbar respectively. Equipment verification was achieved through the reproduction of experimental data for the ethanol/1-butanol system at 1.013bar. The vapour and liquid samples for all nine systems were analysed by gas chromatography with a maximum compositional error of ±0.022 mole fraction. All reported data were found to be thermodynamically consistent using both the L/W and McDermott-Ellis consistency tests. When paired with a common n-alkane, all three structural heptanone isomers displayed similar qualitative trends in phase behaviour. Minimum boiling azeotropes were measured in all nine systems; in the high alkane region for n-octane systems (~98 mole%), the equal concentration region for n-nonane systems (34 mole% to 53 mole%) and in the very dilute n-alkane region for n-decane systems (~3 mole%). The n-nonane systems in particular highlighted the effect of shifting functional group, with completely separate phase envelopes away from the pure alkane composition space evident in a particularly small temperature range. Modelling was performed using in-house developed software, with pure component parameters generated for each system using five different regression procedures. The first was traditional fitting of the segment diameter (σ), segment number (m), segment energy (є/k) and the respective polar parameter (xp, np) to DIPPR correlations of pure component saturated vapour pressure, liquid density and the heat of vaporisation. The latter four procedures included the fixing of the polar parameter according to functional group correlations and the three instances of including the binary VLE data set for each of the three alkanes considered in this work. When applied to the nine binary ketone-alkane systems measured in this work, excellent predictions of the experimental data were in evidence in most cases and only small binary interaction parameters were necessary to correlate the data where pure predictions were poor. The performance of the parameter sets based on the fixing of the polar parameter and the inclusion of VLE data were consistent and of a high quality for both models, with near identical parameters generated in all four cases for each of the nine systems. The parameter sets generated in this fashion were shown to be applicable not only to the systems measured in this work, but also successfully predicted the independently measured experimental data of the n-hexane/4-heptanone system. It was thus concluded that either of these regression alternatives are viable for the generation of accurate component parameters, and the choice of VLE data set included is trivial. The pure predictions of the sPC-SAFTGV model were generally better than its sPC-SAFTJC counterpart, particularly in the case of the traditionally regressed parameter sets. sPC-SAFTGV displayed constant qualitative agreement with the experimental data for each of the heptanone isomers with a given n-alkane. The quality of the predictions of sPC-SAFTJC, however, worsened significantly as the polar interactions diminished from 2- to 4-heptanone, with no predictions even possible for the least polar isomer. This was attributed to the different perturbation theories used in the development of these terms, but a more detailed study would be necessary to confirm this. This work thus shows an apparent inability of the sPC-SAFTJC equation of state to account for the decreasing polar interactions associated with the carbonyl group in a ketone molecule shifting centrally, while sPC-SAFTGV produces qualitatively good fits for all three isomers. These flaws can be overcome through the incorporation of VLE data in the regression procedure if such data is available, or otherwise through the use of group specific correlations for fixing the polar parameter value. / AFRIKAANSE OPSOMMING: Sedert Johannes van der Waals die eerste wiskundige verhouding ontwikkel het wat beide die damp- en vloeibare fases van 'n mengsel by ewewig kon voorspel, is die veld van termodinamiese modellering al deeglik ondersoek. Na die koms van die moderne rekenaars het hierdie vergelykings van hul nederige empiriese wortels gegroei tot die omvattende, fundamentele modelle wat ons vandag het. Een so 'n fundamenteel gebaseerde familie van vergelykings is die ‘Statistical Associating Fluid Theory’ (SAFT) modelle, wat afgelei is vanaf molekulêre versteuringsteorieë, ontwikkel in die 1980s. Hierdie relatiewe jong modelle het in die afgelope ruk aansienlike aanpassing en optimering ondervind. Modelvariante van besondere belang tot hierdie werk, is die vereenvoudigde versteurde ketting of ‘simplified perturbed chain’ SAFT vergelykings, met Jog & Chapman (sPC- SAFTJC) en Gross & Vrabec (sPC- SAFTGV) polêre terme. In die sPC-SAFT toestandsvergelyking word elkeen van die polêre terme ondersteun deur een polêre veranderlike. Hierdie veranderlike is afhanklik van die aantal polêre segmente in die verwysingsvloeistof, maar nie noodwendig hul posisie in die koolstofketting nie. Daarteen is dit bekend dat die polêre interaksies tussen molekules swakker word soos die polêre groep wegbeweeg van die terminale metielgroep, en steriese hindernis ʼn groter rol begin speel. Dus is die vraag of die model die verandering in die polêre interaksie, as gevolg van veranderende posisie van die polêre groep, kan voorspel deur in plek van ʼn posisie afhanklike parameter, slegs ʼn aanpassing van die polêre waardes van die suiwer komponente te maak. Die karbonielgroep in ketoon molekules is een so 'n polêre groep, en ʼn homoloë reeks ketone word in hierdie studie ondersoek. Die afname in die polêre interaksie soos wat die karbonielgroep in 'n ketoon molekule weg skuif vanaf die terminale metiel groep is sigbaar deur die afname in kookpunt van die verskillende isomere. Hierdie effek van die funksionele groepsposisie op binêre fasegedrag is nog nie voorheen vir enige stelsels geëvalueer nie en geen eksperimentele data is vrylik beskikbaar nie. Om hierdie tekortkoming in die literatuur aan te spreek, is eksperimentele fase ewewig data gemeet. ʼn Reeks stelsels is ondersoek wat elk bestaan uit ʼn struktuurisomeer van ʼn mid-lengte ketoon en ʼn tweede komponent met geen funksionele bydrae. Eksperimente is so opgestel om die effek van die skuiwende polêre groep op die fasegedrag te isoleer en kwalitatief te ondersoek. Die gegenereerde data is dan gemodelleer met behulp van die polêre sPC- SAFT variante, soos hierbo gespesifiseer, en die vermoëns van elke model is beoordeel. Isobariese binêre fase ewewig data is by 40kPa gemeet vir damp-vloeistof stelsels bestaande uit 2, 3 & 4 heptanoon, gemeng met drie verskillende normaal alkane van vergelykbare kettinglengte (n-oktaan, n-nonaan & n-dekaan). Die apparaat wat gebruik was is 'n dinamiese Gillespie VLE eenheid met temperatuur- en drukakkuraatheid van 0,03°C en 1.6mbar, onderskeidelik. Die akkuraatheid van die toerusting is bevestig deur eksperimentele data vir ʼn etanol/1-butanol stelsel by 1.013bar te reproduseer. Die damp en vloeibare monsters vir al nege stelsels is ontleed deur gaschromatografie met 'n maksimum komposisionele fout van ± 0,022 (molfraksie). Alle data is as termodinamies konsekwent gevind deur van beide die L/W en McDermott-Ellis konsekwentheidstoetse gebruik te maak. Mengsels van die drie strukturele isomere van heptanoon met ʼn gemene n-alkaan het tydens eksperimente soortgelyke kwalitatiewe tendense in fasegedrag getoon. Gedurende eksperimente is die lae kookpunt asiotrope gemeet vir al nege stelsels. Die asiotrope verskyn in die hoë alkaan konsentrasies (~98 mol%) vir n-oktaan stelsels, medium konsentrasies (34 mol% tot 53 mol%) vir n-nonaan stelsels en baie verdunde konsentrasies (~ 3 mol%) vir n-dekaan stelsels. Die n-nonaan stelsels beeld veral die effek van die verskuiwing van die funksionele groep uit, met diskrete fasegrense wat duidelik apart staan van die suiwer alkaan ruimte, binne ʼn klein temperatuurverskil. Modellering van die stelsels is uitgevoer met behulp van sagteware wat in-huis ontwikkel is. Suiwer komponent data is gegenereer vir elke stelsel deur van vyf verskillende regressie prosedures gebruik te maak. Die eerste is die tradisionele passing van die segment deursnee (σ), segment nommer (m), segment energie (є/k) en die onderskeie polêre parameters (xp, np) op DIPPR korrelasies van die suiwer komponent versadigde dampdruk, vloeistof digtheid en die hitte van verdamping. Die oorblywende vier prosedures sluit in die bepaling van die polêre parameter deur funksionelegroep korrelasies, en drie gevalle waar die binêre VLE data vir elk van die drie alkane ingesluit is. Deur hierdie prosedures op die modellering van die nege binêre ketoon/alkaan stelsels toe te pas, is uitstekende passings van die eksperimentele data verkry met slegs baie klein binêre interaksie parameters nodig waar voorspellings minder akkuraat was. Die prestasie van die parameter stelle, gebaseer op die bepaling van die polêre parameter en die insluiting van VLE data, is konsekwent en van 'n hoë gehalte vir albei modelle, met 'n byna identiese parameters gegenereer in al vier gevalle vir elk van die nege stelsels. Die parameter stelle wat op hierdie metode gegenereer is, is nie net toepaslik gevind op eksperimentele data gemeet in hierdie werk nie, maar ook op onafhanklike data vir die n-heksaan/4-heptanoon stelsel. Daar is tot die gevolgtrekking gekom dat beide van die regressie alternatiewe lewensvatbaar is vir die generasie van akkurate suiwer komponent parameters, en dat die insluiting van die VLE data triviaal is. Die suiwer sPC - SAFTGV voorspelling was oor die algemeen beter as die suiwer sPC- SAFTJC model met die voorspelling van data, veral in die geval van passings gedoen met parameters verkry vanaf tradisionele regressie metodes. sPC- SAFTGV het ʼn voortdurende, kwalitatiewe ooreenkoms met eksperimentele data getoon vir elk van die nege stelsels. Daarteen het voorspellings deur sPC- SAFTJC beduidend verswak soos die polêre interaksies afgeneem het vanaf 2- na 4- heptanoon, met geen akkurate voorspelling moontlik vir die minste polêre isomeer nie. Die verskynsel kan toegeskryf word aan die verskil in versteuringsteorieë wat gebruik word in die ontwikkeling van die onderskeie toestandsvergelykings, maar ʼn meer in-diepte ondersoek is nodig om hierdie teorie te bevestig. Hierdie werk toon dus 'n skynbare onvermoë van die sPC - SAFTJC toestandsvergelyking om die verandering in polêre interaksie, as gevolg van die veranderende posisie van die polêre groep, vir die karbonielgroep in ʼn ketoon te voorspel, terwyl die sPC-SAFTGV toestandsvergelyking goeie kwalitatiewe passings vir al drie isomere bied. Hierdie tekortkominge kan oorkom word deur VLE data, indien beskikbaar, in die regressie prosedure in te sluit, of deur die gebruik van groep spesifieke korrelasies vir die aanpassing van die polêre parameter.

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Process monitoring and fault diagnosis are used to detect abnormal events in processes. The early detection of such events or faults is crucial to continuous process improvement. Although principal component analysis and partial least squares are widely used for process monitoring and fault diagnosis in the metallurgical industries, these models are linear in principle; nonlinear approaches should provide more compact and informative models. The use of auto associative neural networks or auto encoders provide a principled approach for process monitoring. However, until very recently, these multiple layer neural networks have been difficult to train and have therefore not been used to any significant extent in process monitoring. With newly proposed algorithms based on the pre-training of the layers of the neural networks, it is now possible to train neural networks with very complex structures, i.e. deep neural networks. These neural networks can be used as auto encoders to extract features from high dimensional data. In this study, the application of deep auto encoders in the form of Restricted Boltzmann machines (RBM) to the extraction of features from process data is considered. These networks have mostly been used for data visualization to date and have not been applied in the context of fault diagnosis or process monitoring as yet. The objective of this investigation is therefore to assess the feasibility of using Restricted Boltzmann machines in various fault detection schemes. The use of RBM in process monitoring schemes will be discussed, together with the application of these models in automated control frameworks. / AFRIKAANSE OPSOMMING: Prosesmonitering en fout diagnose word gebruik om abnormale gebeure in prosesse op te spoor. Die vroeë opsporing van sulke gebeure of foute is noodsaaklik vir deurlopende verbetering van prosesse. Alhoewel hoofkomponent-analise en parsiële kleinste kwadrate wyd gebruik word vir prosesmonitering en fout diagnose in die metallurgiese industrieë, is hierdie modelle lineêr in beginsel; nie-lineêre benaderings behoort meer kompakte en insiggewende modelle te voorsien. Die gebruik van outo-assosiatiewe neurale netwerke of outokodeerders bied 'n beginsel gebaseerder benadering om dit te bereik. Hierdie veelvoudige laag neurale netwerke was egter tot onlangs moeilik om op te lei en is dus nie tot ʼn beduidende mate in die prosesmonitering gebruik nie. Nuwe, voorgestelde algoritmes, gebaseer op voorafopleiding van die lae van die neurale netwerke, maak dit nou moontlik om neurale netwerke met baie ingewikkelde strukture, d.w.s. diep neurale netwerke, op te lei. Hierdie neurale netwerke kan gebruik word as outokodeerders om kenmerke van hoë-dimensionele data te onttrek. In hierdie studie word die toepassing van diep outokodeerders in die vorm van Beperkte Boltzmann Masjiene vir die onttrekking van kenmerke van proses data oorweeg. Tot dusver is hierdie netwerke meestal vir data visualisering gebruik en dit is nog nie toegepas in die konteks van fout diagnose of prosesmonitering nie. Die doel van hierdie ondersoek is dus om die haalbaarheid van die gebruik van Beperkte Boltzmann Masjiene in verskeie foutopsporingskemas te assesseer. Die gebruik van Beperkte Boltzmann Masjiene se eienskappe in prosesmoniteringskemas sal bespreek word, tesame met die toepassing van hierdie modelle in outomatiese beheer raamwerke.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: In modern steelmaking a tundish serves as an important metallurgical reactor to remove inclusions and maintain thermal and chemical homogeneity in the product. In this study the flow behaviour in a four strand tundish was investigated by means of a 1/2 scale water model, based on Froude number similarity, as well as by using numerical modelling. Both the numerical study and physical model were used to characterise residence time distribution (RTD) in the vessel and to calculate properties pertaining to the tundish flow regime. The three different tundish configurations investigated in this study are: a bare tundish with no flow control devices, a tundish with a turbulence inhibitor and a tundish using a turbulence inhibitor with holes in combination with dams. Preliminary investigations focussed on the framework for obtaining an accurate numerical solution within reasonable computational times. The effect of assuming symmetry and dynamically steady flow in the numerical model was shown to be small relative to the effect of grid size and justifiable by the savings in computational time. The grid independence study indicated the importance of using a finer mesh in areas of high velocity gradients to obtain realistic results and also to limit the number of computational cells. A procedure using gradient adaptation was used to refine the mesh automatically in the required regions for different tundish geometries. Results also showed that the inlet boundary of the numerical model should be selected at the ladle outlet, since assuming a flat velocity profile at the nozzle port resulted in significant changes in the RTD response. Comparison of the results obtained using the numerical model with those from physical experiments yielded an average error of less than 10%. This was assumed to be a good prediction, considering the assumptions employed in the numerical model. Both the physical and numerical models showed that a tundish without flow control devices was prone to significant short circuiting. The addition of a turbulence inhibitor was shown to be successful in preventing short circuiting and provided surface directed flow, which is thought to aid inclusion removal in the slag. Additionally, the minimum, peak and mean residence times and plug flow volume fraction were increased significantly, while the dead volume fraction decreased. However, using a turbulence inhibitor with holes in combination with dams showed that this configuration may cause increased refractory wear together with increased risk of slag entrainment due to flow patterns with increased surface turbulence. It also showed that the short-circuiting might not be eliminated completely. This indicates that certain design changes to tundish flow control systems can introduce problems that outweigh the benefits of the altered flow patterns. Furthermore, the numerical method, which was based on the water model, was modified to simulate the high temperature steel process. A very good match was obtained between the results using the two different numerical models. This serves as additional evidence that tundish water modelling based on Froude number similarity provides a good representation of the actual industrial process. Using the numerical model based on the high temperature steel process the effect of turbulence inhibitor shape was studied for four different turbulence inhibitor designs. Results showed the best performance, based on flow characteristic properties and surface turbulence values, was achieved for the design using a rectangular box-like shape with flanges at the top. However, the comparison emphasized the effect of the turbulence inhibitor shape on the flow behaviour, as each design yielded completely different flow patterns. It was also observed that a good turbulence inhibitor provided an optimum amount of turbulent suppression. Insufficient suppression would cause fast flows, which will result in insufficient residence time for inclusion flotation and high surface turbulence values, which may cause slag entrainment. On the other hand, too much suppression may increase the variation between strands. / AFRIKAANSE OPSOMMING: Die verdeeltrog speel ‘n belangrike rol in die moderne staalvervaardigingsproses deur inklusies te verwyder en termiese en chemiese homogeniteit in die produk te verseker. In hierdie studie is die vloeigedrag in ‘n verdeeltrog met vier uitlate bestudeer deur middel van ‘n 1:2-skaal watermodel, gebaseer op Froude-getal gelykheid, sowel as deur numeriese modellering. Beide die numeriese en watermodel is gebruik om die verblyftyd-distribusie in die trog te karakteriseer en om waardes te bereken wat die vloeigedrag in die verdeeltrog beskryf. Drie verskillende verdeeltrog-opstellings is in hierdie studie bestudeer, naamlik: ‘n leë verdeeltrog met geen vloeibeheertoestelle nie, ‘n verdeeltrog met ‘n turbulensie- inhibeerder en ‘n verdeeltrog wat gebruik maak van ‘n turbulensie-inhibeerder met gate, gekombineer met lae damwalle. Vroeë ondersoeke het gefokus op ‘n metode om akkurate numeriese resultate binne aanvaarbare tye te verkry. Die invloed van die aannames van simmetrie en dinamiese gestadigde vloei op die resultate is bepaal om klein te wees teenoor dié van die roostergrootte. Die gebruik van die aannames is dus geregverdig deur die afname in berekeningstyd wat dit meebring. Die roosteronafhanklikheidstudie het getoon dat dit belangrik is om die vloeivergelykings oor klein volume-eenhede op te los in areas van hoë snelheidsgradiënte, beide om realistiese resultate te verseker en om die aantal volume-eenhede te beperk. ‘n Prosedure wat gebruik maak van gradiëntaanpassing is gebruik om die roostergrootte outomaties te verklein in die areas met hoë snelheidsgradiënte vir verskillende verdeeltrog-opstellings. Resultate het ook getoon dat dit belangrik is om die inlaatgrens van die numeriese model by die smeltpot se uitlaat te kies, aangesien noemenswaardige verskille in die verblyftyd-distribusie waargeneem is wanneer ‘n uniforme snelheidsprofiel aanvaar is waar die metaal die verdeeltrog binnegaan. Daar is gevind dat die resultate by die numeriese en watermodelle verskil met ‘n gemiddelde fout van ongeveer 10%. Dit word beskou as ‘n goeie ooreenstemming, as die aannames wat in die numeriese model gebruik word in ag geneem word. Beide die numeriese en watermodelle het getoon dat die metaalvloei in die leë verdeeltrog geneig is om die kortste roete na die uitlate te kies. Deur van ‘n turbulensie inhibeerder gebruik te maak word hierdie probleem opgelos deur die metaalvloei opwaarts te forseer. In die proses neem die minimum-, piek- en gemiddelde verblyftye, sowel as die propvloei volumefraksie, toe, terwyl die dooievloei fraksie afneem. Die turbulensie inhibeerder met die gate en die lae damwalle is egter meer geneig tot erosie van die vuurvaste materiaal en kan ook vloeipatrone veroorsaak wat metaalskuimdruppels in die metaal kan opneem. Verder volg ‘n klein fraksie van die vloei steeds ‘n kortpad na die uitlaat. Hierdie resultate toon dat sekere veranderings aan verdeeltrog vloeibeerheerstelsels nadelige gevolge kan hê wat enige positiewe gevolge uitkanselleer. Verder is die numeriese metode wat tot dusver op die watersisteem gebaseer is, aangepas om die vloei in die hoëtemperatuur staalproses te simuleer. ‘n Baie goeie vergelyking is verkry tussen die resultate wat die twee numeriese modelle voorspel. Hierdie dien as ‘n verdere bewys dat ‘n watermodel, wat op Froude-getal gelykheid gebaseer is, die industriële proses akkuraat kan simuleer. Deur gebruik te maak van die numeriese model van die hoë temperatuur staalproses, is die effek van die turbulensie-inhibeerder se vorm vir vier verskillende ontwerpe bestudeer. Die studie het getoon dat die beste resultate vir vloeikarakteriserende eienskappe en oppervlak- turbulensie verkry is met ‘n reghoekige ontwerp. Die resultate beklemtoon egter die belangrikheid van die invloed van die turbulensie-inhibeerder se vorm op die vloeigedrag in die verdeeltrog, aangesien elke vorm noemenswaardige verskillende vloeipatrone opgelewer het. Daar is opgemerk dat ‘n goeie turbulensie-inhibeerder ‘n optimale hoeveelheid turbulensie onderdrukking veroorsaak. In die geval van te min onderdrukking is die verblyftye te kort en die oppervlak turbulensie te hoog. Te veel onderdrukking kan egter lei tot groot variasie in die eienskappe van die metaal by die verskillende uitlate.

Thesis (MScEng) –Stellenbosch University, 2010 / ENGLISH ABSTRACT: More mining houses are turning their attention to the processing of ore mined from the UG2 reef. This is mainly due to the depletion of the Merensky reef or the low availability of ore from the Platreef. With the higher UG2 ore concentration in the process feed, companies experience more problems with the processing of the ore due to its high chrome content. Although there are various possible solutions to the problems experienced in the processing of UG2 ore, very little of thise solutions are actually implemented in the industry. When smelting chrome-bearing ore, the chrome can go to any of three phases: matte phase, spinel phase or glass phase. If it reports to the furnace matte phase it can lead to problems in the down stream processing. When chrome forms part of the spinel phase it forms a solid, refractory-like material which, to an extent, is an unwanted material inside the furnace. Lastly the chrome can report to the glass phase (liquid phase) which is the more desireable phase to which chrome should report to since it will have little or no impact on downstream processing. There were four main objectives for this research project namely to conduct a literature review to understand the problem of chrome in the smelting process, to do an experimental simulation of a matte and slag phase in one crucible, to interpret the experimental results and compare the experimental results to thermodynamic predictions obtained using FactSageTM. From literature the following aspects were found to be important: Silica structures Research has shown that silica incorporates different metal ions into its structures. When the metal ions are incorporated into the silica structures they are seen as part of the glass phase. By incorporating cations such as chromium into the silica structure the structure is able to maintain its neutral electrical charge. Basicity of slag Oxides once melted will either donate or accept oxide ions. The group of oxides that are in excess will determine whether that specific slag is acidic or non acidic. This is important to our study since the basicity can determine the stability of the spinel phase. Partial pressures The partial pressure of the system is important since it forms part of the equilibrium constant calculations - meaning that partial pressures determine the stability of certain species. Currently different arguments exist as to how the sulphur pressure inside a molten bath is maintained. What is important, however, is that for the system in this research project a log oxygen partial pressure of -8 and a log sulphur partial pressure of -3.5 was chosen. These values were based on previous research done on PGM and copper smelting processes. Chrome deportment Previous research on chrome deportment shows a relationship between temperature and the amount of chromium dissolving into the glass phase as well as an increased chromium(II)oxide solubility (when compared to chromium(III)oxide) in a silicate melt. Regarding slag chemistry and chrome deportment very little work has been published for the system found in the PGM industry but it is mentioned that by adjusting certain slag additives (alumina, lime and silica) the chrome deportment can be manipulated. The scope of this project was to investigate the effect of chromium, lime and silica on chrome deportment. More specifically, the effect of lime. The reason being that lime was originally added as 10%wt of the feed stream in the processing of Merensky ore to act as a fluxing agent. With the new furnace design and higher power densities the slag are maintained at 200oC to 350oC higher than when Merensky ore was smelted. With these higher slag temperatures fluxing agents will play a smaller role meaning that lime additions become less important. Literature studies also showed that additional lime in a slag system can stabilize the spinel structure (which is an unwanted phase). Removing lime would be advantageous out of a chrome presepective as well as an economic point of view. The research was conducted in three sections namely the determination of the time required for this particular system to reach equilibrium, the investigation of different additives on chrome deportment using a controlled atmosphere and synthetic slags and, lastly, a comparison of the experimental results obtained to thermodynamic predictions. For the equilibration studies reaction time periods of 4,7,11 and 16 hours were used. From the results it was found that the alumina crucible dissolved into the glass phase continually. This indicated that equilibrium was not reached. However, a reaction time, rather than an equilibrium time, was chosen where the species and phases had enough time to react. This was based on literature, on observations of species diffusing between the matte and slag phase as well as on two-point analysis (diffusion gradients). A reaction time of nine hours was chosen With the reaction time fixed, the effect of different slag additives on chrome deportment was investigated. For the addition of chrome it was seen that an 1.5%wt increase in the starting material increased the chrome content of the slag phase by 0.025%wt. For the same increase in chromium in the starting materials the chrome content of the spinel phase increased by 2.1% indicating that chromium has a tendency to report to the spinel phase. The increase in chromium had a minor effect on the chrome content of the matte phase, however, since the chrome content only increased from 0.025%wt to 0.028%wt. Plotting the results showed that increasing the lime in the starting material decreases the chromium content in the glass phase. For the 39%wt silica system the chromium content in the glass phase decreased from 0.75%wt to 0.46%wt for an increase in the lime content from 1.7%wt to 7.3%wt. The same trend was seen for the 33%wt silica system. For the spinel phase an increase of 1.27%wt was seen when the lime content of the starting materials was increased from 1.7%wt to 10.1%wt for a 33%wt silica system. The same increase in lime increased the chrome content of the matte phase from 0.03%wt to 0.06%wt for a 33%wt silica system. Silica also proved to affect chrome deportment. Increasing the silica content of the starting materials from 25%wt to 39%wt increased the amount of chromium in the glass phase from 0%wt to 0.46%wt for a 10%wt lime system. The same effect is seen for a lower lime content except that more chromium were incorporated into the silica structure. A silica increase from 32.4%wt to 39%wt resulted in a chromium decrease from 5.2%wt to 0% in the spinel phase for a 10%wt lime system. The same trend was seen for the 1.5%wt lime system. An increase in the silica levels lead to an increase in the chrome level of the matte phase. When silica is increased from 32%wt to 39%wt the chrome content of the matte phase increased from 0.06%wt to 0.07%wt. The last part of the research project entailed the comparison of the trends observed with the experimental results to trends obtained from thermodynamic predictions. FactSageTM is a program that uses model equations to predict the Gibbs free energies for different phases. The program is therefore also able to predict the amount of different phases present at equilibrium. This is called thermodynamic ”optimization”. In section 6 trends that were observed from FactSageTM results are compared to the trends found in the experimental results. It is important to note that it is only trends that are evaluated and not actual values since FactSageTM calculations are for a system that is at equilibrium and (as explained above) this system is not at complete equilibrium. The comparison however was good. Several trends found in the experimental results were confirmed by the results from FactSageTM. These included the relationships of chromium fed versus chromium spinel, lime fed versus chromium spinel, lime fed versus chromium in glass, silica fed versus chromium in glass, silica fed versus chromium in spinel and silica fed versus chromium in matte. To conclude, slag additions can be used to manipulate chrome deportment to an extent. Secondly, FactSageTM can be used for thermodynamic predictions but a proper understanding as well as some form of validation of the specific system investigated is still needed. Due to time constraints and the difficulty of experimentally simulating this multi-phase system in the lab, only a few parameters were investigated. In order to obtain a more complete understanding of the system the effect of partial pressures and temperature should also be investigated.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Biosurfactants are microbially produced molecules that show excellent surface-active properties. Bacillus subtilis ATCC 21332 produces the biosurfactant, surfactin, which exhibits antimicrobial activity against bacteria as well as fungi. Although antimicrobial activity has been exhibited by a number of bacterially produced biosurfactants, notably the rhamnolipid from the pathogen Pseudomonas aeruginosa, the GRAS status B. subtilis makes the use of this organism preferable for large scale bioprocesses. The objectives of this study were to: (1) evaluate the effect of different nutrient conditions on growth and surfactin production; (2) evaluate the growth of B. subtilis ATCC 21332 and associated surfactin production on a hydrocarbon substrate; (3) evaluate the antimicrobial activity of surfactin against Mycobacterium aurum, and (4) to establish whether active growth of B. subtilis ATCC 21332 and associated surfactin production can be extended during fed-batch culture. B. subtilis ATCC 21332 was grown on low-nitrate; phosphate-limited and nutrient rich media with glucose as substrate during shake flask culture. Nitrate, phosphate, glucose and surfactin were quantified by HPLC analyses and growth via CDW and optical density measurements. Growth and surfactinproduction were further evaluated during shake flask cultureon a hydrocarbon substratereplacing the glucose in the nutrient rich medium with an equivalent amount of n-hexadecane. The antimicrobial activity was quantified by growth inhibition of M. aurum. Bioreactor batch and fed-batch studies were conducted to evaluate growth and surfactin production under controlled conditions. The fed-batch experiments included four constant dilution rate (D=0.40h-1; D=0.15h-1; D=0.10h-1 and D=0.05h-1) and two constant feed rate (F=0.40L/h and F=0.125L/h) fed-batch strategies. The nutrient rich medium was used for these experiments and also as the feed medium for fed-batch experiments. A CDW of 12.6 g/L was achieved in the nutrient rich medium during shake flask culture and was 2.5- and 1.6-fold higher than that achieved in the phosphate-limited medium and the lownitrate medium respectively. A surfactin concentration of 652 mg/L was achieved in the nutrient rich medium, while a maximum surfactin concentration of 730 mg/L was achieved in the phosphate-limited medium. A surfactin concentration of only 172 mg/L was achieved in the low-nitrate medium. Subsequently, growth and surfactin production were evaluated on n-hexadecane as sole carbon source. After inoculation, the CDW did not increase over a period of 119 h, which indicated that B. subtilis ATCC 21332 was unable to utilize n-hexadecane for growth and surfactin production. The maximum CDW (27 g/L) and maximum surfactin concentration (1737 mg/L) achieved in the bioreactor batch experiments were 2.1- and 2.6-fold higher respectively than that achieved in the nutrient rich medium during shake flask experiments. These results served as a benchmark for further fed-batch experiments. During the fed-batch phase of the D=0.40h-1 experiment, the biomass further increasedby 9 g/h, which was 3.5-, 3.1- and 5.3-fold higher compared to the fed-batch phases of the D=0.15h-1, D=0.10h-1 and D=0.05h-1 experiments respectively. Similarly, the biomass increased by 10.7 g/h during the fed-batch phase of the F=0.40L/h experiment, which was 4.6-fold higher than that of the F=0.125L/h experiment. The average rate of surfactin production was 633 mg/h during the fed-batch phase of the D=0.40h-1 experiment, 29.4-, 5.4- and 34.2-fold higher compared to the fed-batch phases of the D=0.15h-1, D=0.10h-1 and D=0.05h-1 experiments respectively. Analogously, the average rate of surfactin production (544 mg/h) of the F=0.40L/h experiment was 9.4 fold higher than that of the F=0.125L/h experiment. The antimicrobial assay showed that surfactin inhibits M. aurum growth. An inhibition zone diamater of 4mm was measured at a surfactin concentration of 208 mg/L, which linearly increased to 24mm at a surfactin concentration of 1662 mg/L. High feed flow rate strategies achieved higher rates of biomass increase and surfactin production and will thus decrease the production time required for large scale surfactin production.The antimicrobial activity of surfactin against M. aurum indicates that this biosurfactant has the potential to be used against M. tuberculosis, and as such has the potential to be used in the medical industry to reduce the spread of this, and other deadly diseases. / AFRIKAANSE OPSOMMING: Biosurfaktante is oppervlak-aktiewe molekules wat deur sekere mikro-organismes geproduseer word. Bacillus subtilis ATCC 21332produseer ‘n biosurfaktant genaamd surfactin, wat antimikrobiese eienskappe toon teen bakterieë sowel as fungi.Menige bakterieël geproduseerde biosurfaktante toon antimikrobiese eienskappe, vernaam die rhamnolipied van die patogeen Pseudomonas aeruginosa, maar die algemene veiligheids-status van B. subtilis gee voorkeur aan hierdie organisme vir grootskaalse bioprosesse. Die doelwitte van hierdie studie was: (1) om die effek van verskillende medium samestellings (in terme van voedingstowwe) ten opsigte van bakteriële seldigtheid en surfactin-produksie te evalueer; (2) om die bakteriële seldigtheid van B. subtilis ATCC 21332 en geassosieerde surfactin produksie vanaf ‘n alkaan-substraat te evalueer; (3) om die antimikrobiese aktiwiteit van surfactin teen Mycobacterium aurum te evalueer; (4) om vas te stel of die aktiewe groei van B. subtilis ATCC 21332 en geassosieerde surfactin-produksie gedurende voer-lot kultuur verleng kan word. B. subtilis ATCC 21332 was op lae-nitraat; fosfaat-beperkte en voedingstofryk-media met glukose as substraat in skudflesse gekultiveer. Nitraat, fosfaat, glukose en surfactin was deur hoëdruk vloeistofchromatografie gekwantifiseer en die seldigtheid deur middel van seldroëmassa en optiese digtheid metings. Verder was die groei van B. subtilis, en geassosieerde surfactin produksie, vanaf ‘n alkaan-substraat in skudflesse ge-evalueer deur die glukose in die voedingstofryke medium met ‘n ekwivalente hoeveelheid van n-heksadekaan te vervang. Die antimikrobiese aktiwiteit van surfactin was deur die geїnhibeerde groei van M. aurum gekwantifiseer. Bioreaktor lot en voer-lot studies was uitgevoer om die groei en surfactin produksie onder beheerde toestande te evalueer. Die voer-lot eksperimente het vier konstante verdunningstempos (D=0.40h-1; D=0.15h-1; D=0.10h-1 en D=0.05h-1) en twee konstante voertempos (F=0.40L/h and F=0.125L/h) ingesluit. Die voedingstofryke medium was vir hierdie eksperimente en ook as die voermedium vir dievoer-lot eksperimente gebruik. ‘n Seldigtheid van 12.6 g/L is bereik gedurende skudfleskultuur in die voedingstofryk-media en was 2.5- en 1.6-voud hoër as die seldigthede wat in die fosfaat-beperkte en lae-nitraat media bereik is. ‘n Surfactin konsentrasie van 652 mg/L is bereik in die voedingstofryke medium, terwyl ‘n maksimum surfactin konsentrasie van 730 mg/L in die fosfaat-beperkte medium bereik is. ‘n Surfactin konsentrasie van slegs 172 mg/L is in die lae-nitraat medium bereik.Hierna was bakteriële seldigtheid en surfactin produksie geuvalueer met slegs n-heksadekaan as die enigste koolstof bron. Die bakteriële seldigtheid het geen verandering getoon na inokulasie nie, wat aangedui het dat B. subtilis ATCC 21332 nie die vermoë beskik om n-heksadekaan vir groei en surfactin produksie te gebruik nie. Die maksimum seldigtheid (27 g/L) en maksimum surfactin konsentrasie (1737 mg/L) bereik in die bioreaktor lot eksperimente was 2.1- en 2.6-voud hoër onderskeidelik as dit bereik in die voedingstofryke medium gedurende skudfles eksperimente. Hierdie resultate dien as ‘n basis vir verdere voer-lot eksperimente. Gedurende die voer-lot fase van die D=0.40h-1 het die biomassa verder verhoog teen 9 g/h, wat 3.5-, 3.1- en 5.3-voud hoër was as dit van die D=0.15h-1, D=0.10h-1 en D=0.05h-1 eksperimente onderskeidelik. Die biomassa het soortgelyk tydens die voer-lot fase van die F=0.40L/h eksperiment teen 10.7 g/h verhoog, wat 4.6-voud hoër was as dit van die F=0.125L/h eksperiment. Die gemiddelde tempo van surfactin produksie was 633 mg/h gedurende die voer-lot fase van die D=0.40h-1 eksperiment, 29.4-, 5.4- en 34.2-voud hoër vergeleke met die voer-lot fases van die D=0.15h-1, D=0.10h-1en D=0.05h-1 eksperimente onderskeidelik. Die gemiddelde tempo van surfactin produksie (544 mg/L) was soortgelyk 9.4-voud hoër gedurende die voer-lot fase van die F=0.40L/h eksperimente, vergeleke met die die F=0.125L/h eksperiment. Die antimikrobiese toetse van surfactin teen M. aurum het positief getoets, wat aandui dat surfactin die groei van hierdie organisme inhibeer. ‘n Inhibisie sone deursnee van 4mm was gemeet teen ‘n surfactin konsentrasie van 208 mg/L, wat lineêr verhoog het tot 24 mm teen ‘n surfactin konsentrasie van 1662 mg/L. Hoë voertempo strategieë het hoër biomassa verhogingstempos en surfactin produksie tempos getoon en sal dus die produksietyd aansienlik verkort tydens grootskaalse surfactin produksie. Die antimikrobiese aktiwiteit van surfactin teen M. aurum toon dat hierdie biosurfaktant die vermoë het om gebruik te word teen M. tuberculosis. Daarom het surfactin die potensiaal om gebruik te word in die mediese industrie om die verspreiding van Tuberkulose, en ander dodelike patogene, te voorkom.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: In a first stage atmospheric leach at the Lonmin Marikana base metals refinery, nickel-copper-iron-sulphur Peirce Smith converter matte is leached in recycled electrolyte from the electrowinning section. The electrolyte contains sulphuric acid, copper and nickel sulphates, and a small amount of iron sulphate. The converter matte contains mostly nickel, copper and sulphur (typically 48 %, 28 % and 23 %, respectively), but also minor amounts (<5 %) iron and cobalt. The matte also contains platinum group elements (PGEs) and other precious metals totalling 0.2 – 0.7 % (platinum, palladium, iridium, rhodium, ruthenium, osmium and some gold). The predominant mineral phases are heazlewoodite, chalcocite and a nickel-copper alloy phase, as well as some entrained slag and spinel minerals. The purpose of the first stage leach is to extract nickel, while simultaneously precipitating copper and PGEs contained in the recycled electrolyte. Nickel, cobalt and iron are leached by acid and oxygen. Copper is precipitated by a redox reaction in which copper ions oxidise nickel from the matte. The purpose of this study was to determine the effects of key variables on the performance of the first stage leach (specifically on the removal of PGEs and copper from solution and the overall extraction of nickel) and to improve fundamental understanding of these effects. Batch leaching tests were carried out to investigate the effects of the following factors: availability of oxygen, initial acid concentration, initial copper concentration, iron endpoint (iron content of the matte), solids/liquid ratio and stirring rate. Liquid samples were analysed with Atomic Absorption Spectroscopy (AA) to determine leaching kinetics. Characterisation of solid samples from leach tests by quantitative X-Ray diffraction (XRD) and scanning electron microscopy with an energy dispersive system (SEM-EDS) helped to improve understanding of the leaching mechanism. The oxidative leaching mechanism entails an initial period in which the alloy phase is leached by acid and oxygen, while copper reacts with the nickel-copper-alloy and heazlewoodite phases (which react galvanically with each other) to form a chalcocite precipitate. In a second reaction period, heazlewoodite was transformed to millerite by acid leaching and the particle structure became more porous. The rate of copper precipitation and nickel extraction were faster during the second reaction period than the first reaction period. Some copper leaching occurred once the leachable nickel (60 – 70 %) had been dissolved, provided that the solution was strongly acidic (pH < 2). The non-oxidative leaching mechanism entails a galvanic interaction, between the nickel-copper-alloy and heazlewoodite phases, in which nickel is leached from both phases and copper is precipitated as chalcocite. Leaching by acid was negligible in most non-oxidative tests. An initial fast period of copper precipitation was followed by a second slower period. The decrease in reaction rate can probably be linked to the decreasing availability of the nickel-copper-alloy phase. During non-oxidative leaching, the particle structure remained mostly intact. Copper precipitation kinetics under non-oxidative conditions was found to be slower than under oxidative conditions. The faster copper precipitation kinetics under oxidative conditions is most likely caused by an increase in porosity and reaction area as nickel is leached from the matte by acid and oxygen. The initial acid concentration, solids/liquid ratio and Fe-endpoint were the most important factors determining reaction kinetics under oxidative conditions. Low initial acid concentrations (37 g/L) and a high solids/liquid ratio improved the extent of copper precipitation. Nickel extraction was enhanced by low solids/liquid ratios and high initial acid concentrations (74 g/L). Nickel extraction was significantly less (56 % less in one instance) when leaching high iron mattes (5.7 % Fe) rather than low iron mattes (< 1 % Fe). Copper precipitation was initially faster when leaching a high iron matte, but slower nickel leaching from high iron mattes led to an excess of available acid, which resulted in copper being leached. The results suggest that high iron mattes will lead to poor copper and PGE precipitation in the first stage leach and also to lower nickel extractions. Consequently, Peirce Smith converting at the plant must be carefully controlled to avoid high iron mattes. Under non-oxidative conditions, the solids/liquid ratio and Fe-endpoint were the most important factors. The rate of copper precipitation was faster when a high iron matte was leached, so that a higher percentage copper was precipitated and more nickel was extracted from the matte. / AFRIKAANSE OPSOMMING: As ‘n eerste stap in die Lonmin Marikana basis-metale veredelingsaanleg word nikkel-koper-yster-swawel Peirce-Smith-converter-mat geloog in elektroliet wat hersirkuleer word vanaf die aanleg se koper-elektroplaterings-afdeling. Die loging word by atmosferiese druk uitgevoer. Die elektroliet bevat swawelsuur, koper- en nikkel-sulfate en ‘n klein hoeveelheid ystersulfaat. Die mat bevat hoofsaaklik nikkel, koper en swawel (tipies 48 %, 28 % en 23 %), maar ook klein hoeveelhede (< 5 %) yster en kobalt. Verder maak Platinum Groep Elemente (PGE’s) en ander waardevolle metale (platinum, palladium, iridium, rhodium, ruthenium, osmium en goud) 0.2 % tot 0.7 % van die massa van die mat uit. In terme van minerale bestaan die materiaal hoofsaaklik uit heazlewoodite, chalcocite en ‘n nikkel-koper allooi fase, asook slak en spinel minerale, wat tydens Peirce-Smith-converting weens meesleuring in die mat rapporteer. Die doel van die eerste stadium loog is om nikkel op te los, terwyl koper en PGE’s wat in die elektroliet voorkom presipiteer moet word. Nikkel, kobalt en koper word geloog in reaksies met suurstof en swawelsuur. Koper word presipiteer deur middel van ‘n redoks reaksie waarin koper-ione nikkel in die mat oksideer. Die doel van hierdie studie was om die effekte van sleutelveranderlikes op die proses te bepaal (spesifiek hoe nikkel-loging en koper presipitasie affekteer word) en om fundamentele begrip van die veranderlikes en hul effekte te verkry. Lot loogtoetse is uitgevoer op ‘n laboratorium-skaal en die effekte van die volgende faktore is ondersoek: beskibaarheid van suurstof, begin suurkonsentrasie, yster eindpunt (die ysterinhoud van die mat), vastestof/vloeistof verhouding en die roertempo. Vloeistof monsters geneem tydens loogtoetse is geanaliseer met behulp van Atoom Absorpsie Spektroskopie (AA) om kinetika te bepaal. Vastestof monsters is ook geneem tydens loogtoetse en kwantitatiewe X-straal diffraksie (XRD), asook skanderings-elektron-mikroskopie met ‘n energie dispersie sisteem (SEM-EDS) is gebruik om die materiaal te karakteriseer en die logingsmeganisme te verduidelik. Die oksidatiewe logingsmeganisme behels ‘n aanvanklike periode waartydens die allooi fase geloog word deur suur en suurstof, terwyl koper presipiteer om chalcocite te vorm as gevolg van ‘n reaksie waarin galvanise interaksie tussen die nikkel-koperallooi en heazlewoodite fases ‘n belangrike rol speel. In ‘n tweede reaksie periode is heazlewoodite geloog deur suur om millerite te vorm. Tydens hierdie tweede fase het die partikel struktuur meer porieus geword. Die tempo van koper presipitasie en nikkel loging was vinniger tydens die tweede reaksie periode as tydens die eerste. Koper is geloog indien die oplossing baie suur was (pH < 2) en die loogbare nikkel (60 – 70 %) reeds opgelos het. Die nie-oksidatiewe logingsmeganisme behels galvaniese interaksie tussen die nikkel-koper-allooi en heazlewoodite fases, wat lei tot koper presipitasie as chalcocite. Loging deur swawelsuur was onbeduidend. ‘n Aanvanklike vinnige periode van koper presipitasie tydens nie-oksidatiewe toetse is gevolg deur ‘n tweede stadiger periode. Die afname in reaksietempo kan waarskynlik verklaar word deur die afnemende beskikbaarheid van die nikkel-koper-allooi fase. Tydens nieoksidatiewe loging het die partikel struktuur redelik onveranderd gebly. Koper presipitasie kinetika in nie-oksidatiewe toetse was stadiger as in oksidatiewe toetse. Die belangrikste faktore wat kinetika in oksidatiewe toetse beïnvloed het was die suurkonsentrasie, vastestof/vloeistof verhouding en die yster-eindpunt. Lae beginsuurkonsentrasies (37 g/L) en ‘n hoë vastestof/vloeistof verhouding het gelei daartoe dat meer koper uit die elektroliet herwin is. Nikkel ekstraksie was hoër indien die vastestof/vloeistof verhouding laag was en die begin suurkonsentrasie hoog (74 g/L). Nikkel ekstraksie was beduidend laer (56 % laer in een geval) wanneer hoë-yster mat (5.7 % Fe) geloog is, eerder as lae yster mat (< 1 % Fe). Wanneer ‘n hoë yster mat geloog is, was koper presipitasie aanvanklik vinniger, maar weens stadige nikkel-ekstraksie-tempos was ‘n oormaat van suur beskikbaar sodat koper uiteindelik geloog is. PGE presipitasie is ook nadelig beïnvloed wanneer koper geloog is en veral tydens toetse met hoë yster mat. Die mees belangrike faktore wat nie-oksidatiewe loging beïnvloed het was die vastestof/vloeistof verhouding en die yster-eindpunt. Die tempo van koper presipitasie was vinniger in toetse met ‘n hoë yster mat, sodat ‘n hoër persentasie koper presipiteer het en meer nikkel opgelos het wanneer ‘n hoë yster mat geloog is.

An investigation was done into the recovery of invert sugar from sugar cane molasses. A pilot plant was designed and constructed to evaluate the clarification and separation of molasses to produce invert sugar syrup. The aim of the pilot plant was to prove the process and deliver data so as to facilitate the design and prove the financial viability of a commercial plant. The pilot plant had to process 300 kg/day of molasses. The clarification of molasses by centrifugal separation, a known desludging process, did not produce a product of acceptable quality which could be used in a chromatographic separator. The results were disappointing. The product obtained was also not suitable for dead end pressure filtration. The turbidity remaining after the centrifugal separation also did not respond to a second flocculation process. Conventional settling clarification was investigated. Seven factors that could influence the consolidation and settling of suspended solids in molasses were identified, namely: the age of the diluted molasses, the temperature of the flocculated mixture, the variations across various batches of flocculant, the effect of reaction time of the phosphoric acid, the optimum flocculant dosing concentration, the optimum concentration of the molasses solution and the effect of increasing the acid dosage. The optimum conditions to clarify molasses through settling were found to be: fresh molasses, at 28 Brix and 60°C, allowing 10 min intervals between acidification with 3,75 g (as 100%) phosphoric acid/ kg dry material (assumed equal to Brix) and neutralisation with 5 g (as 100%) caustic/kg dry material (assumed equal to Brix), flocculation with any batch of flocculant 6195, dosed as a 1000 ppm solution. Commercial equipment was evaluated. The pilot plant E-cat clarifier was operated at 300 l/h and a thick sludge formed. The overflow was clear and it could be filtered. The molasses obtained was suitable for chromatographic separation. The recovery of sugars from molasses sludge has economic merit. From the evaluation of centrifugal separation and gravity separation it is clear that gravity separation again is the best method. The sweet-water obtained is consistent within the clarity requirement of 10 NTU/Brix and can be used to dilute raw molasses in the upstream processing step. The clarification process that was developed is patented. [Bekker, Stolz et.al. (2001)] A sugar recovery of 93.9 mass % at a purity of 99.7 mass % from molasses, was achieved using a simulated moving bed, ion exclusion, pilot plant. The operating conditions for this performance were: feed flow at 14 l/h and at a temperature above 60 °C; water flow at 63 l/h and at a temperature above 65 °C; extract flow at 21 l/h; raffinate flow at 56 l/h; loop flow at 78 l/h and step time at 1326 seconds. This relates to the following bed volumes of the various separation zones: Bed Volume Zone 1 = 0.694; Bed Volume Zone 2 = 0.591; Bed Volume Zone 3 = 0.661; Bed Volume Zone 4 = 0.383. There is a trade-off between purity and recovery and a reduction in water usage. A preliminary environmental impact assessment and conceptual mass balance were done. The proposed plant integrates well into the existing Komati Mill of TSB and does not pose any significant environmental threat. The plant requires certain services from the mill. The mass balance investigated the water and steam consumption of the plant. Process integration was done so as to obtain the optimum utility consumption. The utility consumption of the plant does not exceed the capacity available at the mill. A small boiler is however required to produce steam during the annual mill maintenance period. Various techniques were used in a cost estimation for the invert sugar plant. The internal rate of return (IRR) is 42% for a fixed capital investment of R94,270,000.00. The net return rate (NRR) for the project is 4%/year, the net present value (NPV) - discounted at a 30% cost-of-capital is R41,782,000.00. The net payout time (NPT) is 5.207 years. The project fulfils the financial requirements set by TSB. It is now possible and viable to desugarize cane molasses.

Thesis (MScEng)--Stellenbosch University. / ENGLISH ABSTRACT: Carbon dioxide (CO2) is classified as the main greenhouse gas (GHG) contributing to global warming. Estimates by the Intergovernmental Panel on Climate Change (IPCC) suggest that CO2 emissions must be reduced by between 50 to 85% by 2050 to avoid irreversible impacts. Carbon capture and storage (CCS) strategies can be applied to de-carbonize the emissions from fossil-fueled power plants. Compared to other CCS techniques, post-combustion capture (PCC) is most likely to be implemented effectively as a retrofit option to existing power plants. At present however CCS is not yet commercially viable. The main challenge with CCS is to reduce the inherent energy penalty of the CO2 separation stage on the host plant. Seventy-five to eighty percent of the total cost of CCS is associated with the separation stage. There are several technologies available for separating CO2 from power plant flue gas streams. Reactive absorption with aqueous amine solutions has the ability to treat low concentration, low pressure and large flux flue gas streams in industrial-scale applications. It is most likely to be the first technology employed commercially in the implementation of CCS. The energy required for solvent regeneration however, is high for the standard solvent used in reactive absorption processes, i.e. MEA. This leads to a reduction in thermal efficiency of the host plant of up to 15%. Alternative solvent formulations are being evaluated in an attempt to reduce the energy intensity of the regeneration process. The main objective of this study was to establish a novel, simplified thermodynamic method for solvent screening. Partial solubility parameters (PSPs) were identified as the potential basis for such a method. The major limitation of this approach is that the model doesn’t account for effects from chemical reaction(s) between materials, e.g. CO2 reacting with aqueous alkanolamine solutions; considering only the effects from dissolution. The EquiSolv software system was developed based on PSP theory. The Hansen 3-set PSP approach was used to describe the equilibrium behaviour of CO2 absorbing in task specific solvents. The Hansen theory was expanded to a 4-set approach to account for contributions from electrostatic interactions between materials. The EquiSolv program was used successfully to screen large sets of solvent data (up to 400 million formulations) in the search for suitable alternative solvent formulations for CO2 absorption. The secondary objective of this study was to evaluate the ability of the proposed PSP model to accurately predict suitable alternative solvents for CO2 absorption through preliminary experimental work. A series of CO2 absorption experiments were conducted to evaluate the absorption performance of predicted alternative solvent formulations. The predicted alternative solvent formulations exhibited a significant improvement in absorption performance (up to a 97% increase in the measured absorption capacity) compared to conventional solvent formulations. Statistical analysis of the experimental results has shown that there is a statistically significant concordant relationship between the predicted and measured rankings for the absorption performance of the predicted solvent formulations. Based on this it was concluded that PSP theory can be used to accurately predict the equilibrium behaviour of CO2 absorbing in task specific solvents. Recently ionic liquids (ILs) have been identified as potential alternatives to alkanolamine solutions conventionally used for CO2 absorption. Absorption experiments were conducted as a preliminary assessment of the absorption performance of ILs. Results have shown ILs to have significantly improved performance compared to conventional alkanolamine solvents; up to a 96% increase in the measured absorption capacity compared to conventional solvents. Future work should focus on developing task specific ionic liquids (TSILs) in an attempt to reduce the energy intensity of solvent regeneration in CO2 absorption processes. / AFRIKAANSE OPSOMMING: Koolsuurgas (CO2) word geklassifiseer as die vernaamste kweekhuis gas (GHG) wat bydra to globale verwarming. Beramings deur die Interregeringspaneel oor Klimaatsverandering (IPKV) toon aan dat CO2 emissies teen 2050 verminder moet word met tussen 50 en 85% om onomkeerbare invloede te vermy. Verskeie koolstof opvangs en bergings (KOB) strategieë kan toegepas word ten einde die koolstof dioksied konsentrasie in die emissies van kragstasies wat fossielbrandstowwe gebruik, te verminder. Naverbranding opvangs (NVO) is die mees aangewese KOB tegniek wat effektief toegepas kan word op bestaande kragstasies. Tans is KOB egter nog nie kommersieël lewensvatbaarvatbaar nie. Die hoof uitdaging wat KOB in die gesig staar is om die energie boete inherent aan die CO2 skeidingstap te verminder. Tussen vyf-en-sewentig en tagtig persent van die totale koste van KOB is gekoppel aan die skeidingstap. Daar is verskeie metodes beskikbaar vir die skeiding van CO2 uit die uitlaatgasse van kragstasies. Reaktiewe absorpsie met waterige oplossings van amiene kan gebruik word om lae konsentrasie, lae druk en hoë vloei uitlaatgasstrome in industriële toepassings te behandel. Dit is hoogs waarskynlik die eerste tegnologie wat kommersieël aangewend sal word in die toepassing van KOB. Die oplosmiddel wat normalweg vir reaktiewe absorpsie gebruik word (d.w.s. MEA) benodig egter ‘n groot hoeveelheid energie vir regenerasie. Dit lei tot ‘n afname in die termiese doeltreffendheid van die voeder aanleg van tot 15%. Alternatiewe oplosmiddelstelsels word tans ondersoek in ‘n poging om the energie intensiteit van die regenerasieproses te verminder. Die hoof doelwit van hierdie studie was om ‘n nuwe, ongekompliseerde termodinamiese metode te vestig vir die keuring van alternatiewe oplosmiddels. Parsiële oplosbaarheidsparameters (POPs) is geïdentifiseer as ‘n moontlike grondslag vir so ‘n metode. Die model beskryf egter slegs die ontbindings gedrag van materiale. Die effekte van chemise reaksie(s) tussen materiale, bv. die tussen CO2 en waterige oplossings van alkanolamiene, word nie in ag geneem nie. Die POP teorie het gedien as grondslag vir die ontwerp van die EquiSolv sagteware stelsel. Die Hansen stel van drie POPs is gebruik om die ewewigsgedrag te beskryf van CO2 wat absorbeer in doelgerig-ontwerpte oplosmiddels. Die Hansen teorie is verder uitgebrei na ‘n stel van vier POPs om die bydrae van elektrostatiese wisselwerking tussen materiale in ag te neem. Die EquiSolv program is verskeie kere met groot sukses gebruik vir die sifting van groot stelle data (soveel as 400 miljoen formulasies) in die soektog na alternatiewe oplosmiddels vir CO2 absorpsie. Die sekondêre doelwit van die studie was om die vermoë van die voorgestelde POP model om geskikte alternatiewe oplosmiddels vir CO2 absorpsie akkuraat te voorspel, te ondersoek deur voorlopige eksperimentele werk. ‘n Reeks CO2 absorpsie eksperimente is gedoen ten einde die absorpsie werkverrigting van die voorspelde alternatiewe oplosmidels te ondersoek. ‘n Verbetering in absorpsie werkverrigting van tot 97% is gevind vir die voorspelde oplosmiddels vergeleke met die van oplosmiddels wat tipies in die industrie gebruik word. Statistiese ontleding van die eksperimentele resultate het getoon dat daar ‘n beduidende ooreenstemming tussen die voorspelde en gemete rangskikking van die voorspelde oplosmiddels se werkverrigting bestaan. Dus kan POP teorie gebruik word om die absorpsie van CO2 in doelgerig-ontwerpte oplosmiddels akkuraat te beskryf. Ioniese vloeistowwe (IVs) is onlangs geïdentifiseer as moontlike alternatiewe oplosmidels vir die alkanolamien oplossings wat normaalweg gebruik word vir CO2 absorpsie. Absorpsie eksperimente is gedoen ten einde ‘n voorlopige raming van die absorpsie werkverrigting van IVs te bekom. Daar is bevind dat IVs ‘n beduidende verbetering in werkverrigting toon in vergelyking met die alkanolamien oplosmiddels wat normaalweg gebruik word. ‘n Verbetering in absorpsie werkverrigting van tot 96% is gevind vir die voorspelde IV-bevattende oplosmiddels vergeleke met die van oplosmiddels wat tipies in die industrie gebruik word. Die fokus van toekomstige navorsing moet val op die ontwikkeling van doelgemaakte ioniese vloeistowwe (DGIVs) in ‘n poging om die energie intensiteit van oplosmiddel regenerasie in CO2 absorpsie prosesse te verminder.

Thesis (MIng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: TheSouthAfrican economy islargely dependant on small enterprisesas a valuable source of job creation, gross domestic product as well as product development and innovation, However, unfortunately there existsan extremeiy high failure rate among small businesswith 20%of startup businessesfailing within the firstyear of operation, and an almost 60% failure rate within the first6 years of existence, Thesestatisticshave initiated several research studies,and have been the focus of many businessbooks, in itseif, creating a vast industry of small businesssuccesstools and quick fix solutions, When considering the high failure rates of small businesses,the concepts surrounding sustainable development come into question by pure method of association, Sustainable development issueshave become a top priority globally and have moved up the corporate agenda in recent years. When trying to "marry" these two concepts, questions arise regarding the effect of integrating sustainability principles and management systems,with contemporary small businessstrategy. Theaim of thisstudy isto investigate existingcritical successmodels and to integrate some simple initial stages of sustainable development business strategy within these models. Expectantly, some of the principles contained in the formalisation of management systems that address sustainability issues,could be incorporated in traditional management models in an attempt to identify possible interventions and tools that might positivelyimpact on the successrate of small businessenterprises. These concepts would be tested by means of implementing a formal environmental management system (based on the ISO 14001standard) as an initial approach to addressingsustainabilitygoals, as a case study, The successful implementation of an ISO 14001 environmental management system at this small businessenterprise, realised several advantages for the company, and have been used to adapt traditional management models to include for some of the simple concepts of sustainable development. / AFRIKAANSE OPSOMMING: Die Suid Afrikaanse ekonomie is in 'n groot mate afhanklik van klein besighede as 'n waardevolle bron van werkskepping, bruto binnelandse produk, asook van produk ontwikkeling en innovasie, Des nieteenstaande, bestaan daar ongelukkig 'n baie hoe faling syfer onder klein besighede, met 20%van aanvangsbesighede wat mislukbinne die eerste jaar van bedryf en ongeveer 60%van besighede wat mislukbinne die eerste 6jaar van bestaan. Hierdie statistieke het reeds verskeie navorsingstudiesgeinisieer en was reeds die tema van verskeie boeke, wat opsig self 'n reuse industrie genereer van sake sukseshandleidings en kits oplossings vir verskeie probleme, Wanneer hierdie hoe falings statistieke onder klein sake ondernemings oorweeg word, bevraagteken mens die konsepte rakende volhoubare ontwikkeiing, bloot as gevolg van assosiasie,Volhoubare ontwikkeling het in die laaste paar jaar baie aandag geniet op die prioriteitsagendas internationaal, asook van verskeie korporatiewe agendas. As gepoog word om hierdie twee konsepte met mekaar te vereenselwig, ontwikkel daar verskeievrae rakende die effek van die integrering van volhoubare ontwikkelingsbeginselsen verwante bestuurstelsels,met bestaande kiein sake onderneming strategie, Die doel van hierdie studie isom bestaande suksesmodelIe vir klein sake ondernemings te ondersoek, en om sommige van die begin fase beginselsvan volhoubare besigheids strategie, met mekaar te integreer. Daar sou verwag kon word dot sommige van .die konsepte bevat in die formaiisering van bestuurstelselsrakende volhoubare ontwikkeling, ook geinkorporeer kan word binne bestaande traditionele bestuursmodelle, in 'n poging om moontlike ingrypings en gereedskap te identifiseer wat 'n positiewe impak kan he op die suksessyfersvan kleinsake ondernemings. Hierdie konsepte is getoets aan die hand van 'n implimentering van 'n formele omgewingsbestuurstelsel(gebasseer op die ISO14001standaard) as 'ngevalle studie, wat die begin benadering vorm om die doelwitte van volhoubaarheid aan te spreek. Die suksesvolleimplimentering van 'n ISO 14001omgewingsbestuurselsel by 'n klein sake onderneming het verskeie voordele vir hierdie maatskappy tot gevolg gehad. en is gebruik om tradisionele suksesmodelleaan te pas, om voorsiening te maak vir sommige van die konsepte rakende volhoubare ontwikkeling.

Thesis (MScEng (Process Engineering))--Stellenbosch University, 2008. / This report covers the development of a biofuels engine testing facility at Stellenbosch University. The motivation for the project was three fold: a) a desire to establish biofuels and engine testing know-how; b) to test the performance characteristics of biodiesel; and c) make a facility available for future research. The two main conclusions drawn from the initial test results are: 1) the test cell is fully operational and 2) biodiesel can be substituted for mineral diesel. To the author’s knowledge this is the first biofuel specific engine testing facility in South Africa. After a literature study the test cell was realised in three phases. • Firstly, the hardware layout was designed and the necessary equipment was sourced from respectable suppliers including the judicious use of good qaulity second hand components to minimize capital cost. • The test cell was then instrumented with new sensors. Key components among these are the K-type thermocouples, barometric pressure, humidity, oil pressure and an Allen-Bradley programmable controller to serve as a data acquisition card. Two software programs were chosen, ETA for the control of the test cell and RSLogix to program the programmable logic controller (PLC). • The complete system was then integrated, debugged and validated. The design methods and procedures have been documented throughout the project along with user manuals to facilitate further research. To determine the difference in combustion parameters between biodiesel and mineral diesel an autonomous power curve test was conducted. This revealed little difference in terms of performance between the two fuels, although biodiesel had on average a marginal 0.4% decrease in power over mineral diesel. The fuel consumption for pure biodiesel was found to be higher, which is as expected as it is has a lower calorific value than mineral diesel. As a final validation, an energy balance was conducted. Here the calculated calorific value of biodiesel was compared to the results from a calorie bomb test, and the two results were found to be within 2% of each of other. / Centre for Renewable and Sustainable Energy Studies