Thesis (MScEng)--University of Stellenbosch. / ENGLISH ABSTRACT: Aerosol synthesis involves the formation of condensable product species by gas-phase reaction, and the simultaneous growth of particles by coagulation. For the production of ceramic particles, reaction temperatures higher than 700 K are commonly used, and a maximum fusible particle size is observed. Coagulation-controlled growth yields spherical particles up to the maximum fusible size (approximately < 50 nm). Such particles coalesce rapidly and completely upon collision with other particles, whereas larger particles reach a meta-stable equilibrium for solid-state coalescence. Agglomerates with weak Van der Waal's bonds between particles inevitably form in the cooling/collection process. Coagulation of particles larger than the maximum fusible particle size yields agglomerates with significant neck growth between the primary particles. Spherical ceramic particles in the order of 1 J-Lm are favourable precursors for bulk electronic applications that require high purity. Such large spherical particles may possibly be produced in conditions of seed growth, which involves the deposition of small newly formed clusters onto larger existing particles. The central focus of the present work is to evaluate whether spherical ceramic particles significantly larger than the maximum fusible size may be produced by seed growth. The evaluation is done by modelling of process constraints and interpretation of published results. The modelling of constraints is based on a mathematical framework for comparison of different values of reactor design parameters. This framework comprises a simplified model system, a typology of quantities, and isolation of a set of independent design parameters. Comparison is done on the basis of fixed initial (seed) and final (product) particle sizes. The reactor design framework is used to evaluate the hypothesis on spherical seed growth, by assessing whether a reactor can be designed that satisfies all the process constraints. Future extension of the framework may allow optimisation for seed growth in general. The model system assumes laminar flow and isothermal conditions, and neglects the effect of reactor diameter on wall-deposition. The constraints are graphically represented in terms of the design parameters of initial reactant concentration and seed concentration. The effects of different temperatures and pressures on the constraints are also investigated. In a separate analysis, the suitability of turbulent flow for seed growth is assessed by calculating Brownian and turbulent collision coefficients for different colliding species. As turbulent intensity is increased, the seed coagulation rate is the first coagulation rate to be significantly enhanced by turbulence, resulting in a lowering of the maximum seed concentration allowed by the constraint for negligible seed coagulation. This tightening of a constraint by turbulence is the justification for considering only laminar flow for evaluating the hypothesis on spherical seed growth. Quantitative application of the model of constraints, as well as experimental and modelling results from the literature, did not demonstrate that significant spherical seed growth is possible without seed coagulation (agglomeration). As part of the conceptual effort in becoming familiar with aerosol reactor engineering, a simple two-mode plug-flow aerosol reactor model was developed, and verified with published results. This model has some novel value in that it translates the equations for aerosol dynamics into the terminology of reactor engineering. / AFRIKAANSE OPSOMMING: Aerosol sintese behels die gelyktydige chemiese vorming van 'n kondenseerbare spesie en die groei van partikels deur koagulasie. Temperature hoër as 700K word gewoonlik vir die aerosol sintese van keramieke gebruik. Partikels bo 'n sekere grootte kan nie saamsmelt nie. Koagulasie- beheerde groei lewer sferiese partikels tot en met die maksimum saamsmeltbare partikelgrootte (ongeveer < 50 nm). Wanneer sulke partikels bots, smelt hulle vinnig en volledig saam. Groter partikels bereik egter 'n meta-stabiele ewewig vir vastestof samesmelting. Agglomerate met swak Van der Waal's bindinge tussen partikels vorm onvermydelik wanneer die aerosol afgekoel word en die produk versamel word. Koagulasie van partikels groter as die maksimum saamsmeltbare grootte, lewer agglomerate met noemenswaardige nekvorming tussen primêre partikels. Sferiese keramiekpartikels in die ordegrootte van 1Mmis geskikte intermediêre produkte vir die vervaardiging van soliede eletroniese komponente waarvoor hoë materiaalsuiwerheid vereis word. Sulke groot sferiese partikels kan moontlik geproduseer word in toestande waar klein nuutgevormde partikels deponeer op groter bestaande partikels (saadpartikels). Die hoof-fokus van die huidige werk is om vas te stelof sferiese keramiekpartikels wat noemenswaardig groter is as die maksimum saamsmeltbare grootte, geproduseer kan word met die metode van saadpartikel-groei. Die moontlikheid word ondersoek deur 'n model van prosesbeperkings te maak, en deur gepubliseerde resultate te vertolk. Die model van prosesbeperkings is gegrond op 'n wiskundige raamwerk vir die vergelyking van verskillende waardes van reaktor ontwerp-parameters. Hierdie raamwerk bestaan uit 'n vereenvoudigde model-sisteem, 'n tipologie van verskillende soorte groothede, en die identifikasie van 'n stelonafhanklike ontwerp-parameters. Verskillende parameter-waardes word vergelyk vir dieselfde aanvanklike (saad) en resulterende (produk) partikelgroottes. Die reaktorontwerp-raamwerk word gebruik om die hipotese van sferiese saadpartikel-groei te evalueer, deur vas te stelof 'n reaktor ontwerp kan word wat aan al die prosesbeperkings voldoen. Mettertydse verfyning van die raamwerk kan dit moontlik geskik maak vir die optimering van saadpartikel-groei in die algemeen. Die model-sisteem is gebaseer op die aannames dat vloei laminêr en temperatuur konstant is, en die effek van reaktor-diameter op deponering op die reaktorwand word verontagsaam. Die posesbeperkings word grafies voorgestel in terme van oorspronklike reaktant-konsentrasie en saadpartikel-konsentrasie. Die effek van verskillende temperature en drukke op die prosesbeperkings word ook ondersoek. 'n Systaande ondersoek word gedoen oor die toepaslikheid van turbulente vloei vir saadpartikel- groei, deur botsings-koeffisiënte vir Brown-beweging en turbulensie te vergelyk. Wanneer turbulensie verhoog word, styg die koaguleringstempo van saadpartikels beduidend voordat ander koaguleringstempo's beduidend toeneem. Dit noodsaak 'n verlaging in die maksimum toelaatbare saadpartikel-konsentrasie om saadpartikel-koagulasie te verhoed. Hierdie verskerping van 'n prosesbeperking deur turbulente vloei, is die rede hoekom slegs laminêre vloei beskou word in die evaluering van die hipotese van sferiese saadpartikel-groei. Kwantitatiewe toepassing van die model van beperkings, asook eksperimentele en modellerings- resultate vanuit die literatuur, het nie getoon dat noemenswaardige groei van sferiese keramiekpartikels verkry kan word sonder saadpartikel-koagulasie (agglomerasie) nie. As deel van die proses om aerosol reaktor-ingenieurswese konsepsueelonder beheer te kry, is 'n eenvoudige twee-modus propvloei aerosol reaktor modelontwikkel. Die resultate van die model is bevestig deur vergelyking met gepubliseerde resultate. Hierdie model het die nuwigheid dat dit die vergelykings vir aerosol dinamika uitdruk in die terminologie van reaktor-ingenieurswese.

Thesis (PhDEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Separation processes are an integral part of chemical engineering. The purity of a chemical product is among the principal factors influencing its value. Therefore, any method that can increase the purity of a product or decrease the cost of purification will have a direct effect on the profitability of the entire plant. An important class of separation processes is the solvent-based separations. This includes processes like extractive distillation, liquid-liquid extraction and chromatographic separation. Heterogeneous azeotropic distillation is closely related to these processes. The most important variable in the design of a solvent-based separation process is the choice of solvent. A genetic algorithm for the computer-aided molecular design of solvents for extractive distillation had been previously developed by the author. This algorithm was improved and expanded to include liquid-liquid extraction, heterogeneous azeotropic distillation, gas-liquid chromatography and liquid-liquid (partition) chromatography. At the same time the efficiency of the algorithm was improved, resulting in a speed increase of up to 500% in certain cases. An automatic parameter tuning algorithm was also implemented to ensure maximum efficiency of the underlying genetic algorithm. In order to find suitable entrainers for heterogeneous azeotropic distillation a method is required to locate any ternary heterogeneous azeotropes present in a system. A number of methods proposed in the literature were evaluated and found to be computationally inefficient. Two new methods were therefore developed for ternary systems. A methodology for applying these methods to quaternary and higher systems was also proposed. Two algorithms to design blended solvents were also developed. Blended solvents allow the use of simpler and thus cheaper solvents by spreading the active functional groups over several molecular backbones. It was observed in a number of cases that the blended solvents performed better than their individual components. This was attributed to synergistic interactions between these components. Experimental evidence for this effect was also found. The algorithm was applied to a number of industrially important separation problems, including the extremely difficult final purification process of alpha olefins. In each case solvents were found that are predicted to perform substantially better than those that are currently used in industry. A number of these predictions were tested by experiment and found to hold true. / AFRIKAANSE OPSOMMING: Skeidingsprosesse is 'n integrale deel van chemiese ingenieurswese. Die suiwerheid van 'n chemiese produk is een van die hoof faktore wat die waarde daarvan bepaal. Derhalwe sal enige metode wat die suiwerheid van 'n produk kan verbeter, of die koste van die suiwering daarvan kan verlaag, 'n direkte effek op die winsgewendheid van die hele aanleg hê. 'n Belangrike groep skeidingsprosesse is die oplosmiddel-gebaseerde skeidings. Dit sluit prosesse soos ekstraktiewe distillasie, vloeistofvloeistof ekstraksie en chromatografiese skeidings in. Heterogene azeotrope distillasie is nou verwant aan hierdie prosesse. Die belangrikste veranderlike in die ontwerp van so 'n oplosmiddel-gebaseerde proses is die keuse van oplosmiddel. 'n Genetiese algoritme vir die rekenaargesteunde molekulêe ontwerp van oplosmiddels vir ekstraktiewe distillasie is voorheen ontwikkel deur die skrywer. Hierdie algoritme is verbeter en uitgebrei om vloeistofvloeistofekstraksie, heterogene azeotrope distillasie, gas-vloeistof chromatografie en vloeistof-vloeistof (verdelings) chromatografie in te sluit. Ter selfde tyd is die doeltreffendheid van die algoritme verbeter, wat 'n verbetering in spoed van tot 500% in sekere gevalle tot gevolg gehad het. 'n Algoritme om die parameters van die onderliggende genetiese algoritme outomaties te verfyn is ook geïm plementeer om die optimale werksverrigting van die algoritme te verseker. Om gepaste saamsleepmiddels vir heterogene azeotrope distillasie te vind, word 'n metode benodig om enige ternêre heterogene azeotrope aanwesig in 'n stelsel op te spoor. 'n Aantal sulke metodes wat in die literatuur voorgestel is, is geëvaluEer en daar is gevind dat hierdie metodes ondoeltreffend is. Twee nuwe metodes is derhalwe ontwikkel vir ternêre stelsels. 'n Metodiek om hierdie metodes op kwaternêre en hoër stelsels toe te pas, is ook voorgestel. Twee algoritmes vir die ontwerp van gemengde oplosmiddels is ook ontwikkel. Gemengde oplosmiddels laat die gebruik van eenvoudiger en dus goedkoper oplosmiddels toe, deur die aktiewe funksionele groepe oor 'n aantal molekulêe strukture te versprei. Daar is 'n aantal gevalle waargeneem waar die mengsel beter skeiding bewerkstellig het as die individuele oplosmiddels waaruit dit bestaan. Dit is toegeskryf aan 'n sinergistiese wisselwerking tussen die komponente van die mengsel. Eksperimentele getuienis vir hierdie effek is ook ingewin. Die algoritme is toegepas op 'n aantal belangrike skeidingsprobleme vanuit die bedryf, insluitende die uiters moeilike finale suiwering van alfa olefiene. In elke geval is oplosmiddels gevind wat volgens voorspelling aansienlike beter skeidings sal bewerkstellig as dié wat tans in die bedryf gebruik word. 'n Aantal van hierdie voorspellings is eksperimenteel getoets en korrek bewys.

Thesis (MScEng.)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Slag cleaning has become a common practice at many smelters in the nonferrous industry to maximize recovery of valuable metals. However, during the carbothermic reduction of nonferrous slag to recover cobalt, in particular, iron is recovered predominantly. High iron levels present a problem for the subsequent treatment of the alloy as it may increase the solids loading to the filter and lead to increased reagent consumption during leaching. Finding an appropriate slag modifier that would selectively improve the recovery of cobalt against that of iron to the metallic alloy can solve this problem. In the present study the effects of lime (CaO), rutile (Ti02), and fluorspar (CaF2) on the recovery of cobalt from waste nonferrous slag have been investigated under reducing conditions at 1500°C. The selective recovery of cobalt compared to the recovery of iron at different levels of flux additions is discussed in this study, to show the selectivity of these fluxes. It is also shown in the study that the recovery of cobalt does not only depend on the oxygen partial pressure and temperature but on the slag composition as well. The slags used in the experiments were a) synthetic slag prepared from chemically pure reagents and its composition was derived from that of the industrial nonferrous slag composition typical of reverbaratory furnace and b) actual slag obtained from an old slag dump situated on the Zambian Copperbelt region. The investigation has shown that Ti02 addition leads to the most selective cobalt recoveries in all cases. On the other hand, both CaO and CaF2 lead to higher overall cobalt recoveries. The effect of Ti02 on the slag chemistry leads to the formation of iron titanate compounds in the slag unlike CaO, which displaces "FeO" from the fayalitic slag and thus increases the activity of FeO in the molten slag, which in tum affects the iron recoveries to the alloy product. CaF2 on the other hand, affects the fluidity of the slag leading to improved recoveries by improved settling of metals through the slag to the alloy product. A 44V/I100A DC-plasma arc furnace was used to reduce slag to recover cobalt at about 13.5kV A power input. The major part of the study was conducted in a tube furnace and the findings were applied to the extraction of cobalt from slag using the plasma-arc furnace. It was found that the synthetic slag experiments could be used as a guide to understand the behaviour of cobalt during the carbothermic recovery of cobalt from silica saturated fayalitic slags. Cobalt recoveries were higher in the DC furnace than the corresponding reduction experiments carried out in the tube furnace. However, significant amounts of silicon and carbon were detected in the metallic alloy product of the DC plasma-arc furnace. / AFRIKAANSE OPSOMMING: Slak suiwering is besig om standaard praktyk te word by vele smelters om die herwinning van waardevolle metale uit slak te maksimeer. Tydens die karbotermiese reduksie van slakke vanaf kopersmelters om kobalt te herwin, word beduidende hoeveelhede yster ook herwin. Hoë ystervlakke in die herwinde legering veroorsaak probleme met die stroom-af verwerking van die legering aangesien dit lei tot verhoogde reagensgebruik tydens loging en 'n verhoogde vastestof las of die filterstelsel. Die identifisering van 'n geskikte slak modifiseerder, wat die selektiwiteit van herwinning van kobalt relatief tot yster verhoog, sal hierdie probleem verminder. In hierdie tesis word die rol van kalk (CaO), rutiel (Ti02) en vloeispaat (CaF2) toevoeging tot die selektiewe herwinning van kobalt uit afvalslakke ondersoek. Die karbotermiese reduksie van die slak vind by 1500 °C plaas. Dit word getoon dat bo-en-behalwe die suurstofpotensiaal en die bedryfstemperatuur, die slakchemie 'n beduidende rol speel. Die slakke gebruik in hierdie studie is: a) 'n sintetiese slak gemaak van chemies-suiwer rou-materiale (waarvan die samestelling afgelei is van die samestelling van tipiese reverbereeroond slakke), en b) monsters van die ware slak verkry vanaf 'n slakhoop van die Zambiese Kopergordel. Die studie het getoon dat Ti02 toevoeging gelei het tot die hoogste selektiwiteit in alle gevalle. Daarteenoor het CaF2 en CaO gelei tot hoër algehele herwinnings van kobalt. Ti02 toevoeging lei tot die vorming van ystertitanaat komplekse in die slak, teenoor CaO wat die "FeO" uit die fajaliet struktuur verplaas en die aktiwiteit van FeO in die slak verhoog en dus gevolglik herwinning van yster tot die legering beïnvloed. CaF2 verhoog egter die vloeibaarheid van die slak wat lei tot verhoogde herwinning deurdat die legering druppels makliker uitsak deur die slak. 'n 44VIII OOAGelykstroom-plasmaboogoond is gebruik om die kobalt te herwin uit die slak teen ongeveer 13.5 kVA Die grootste gedeelte van die studie is gedoen in 'n buisoond en die bevindings was dan toegepas op die ekstraksie van kobalt uit slak in die plasmaboogoond. Dit was gevind dat die sintetiese slak eksperimente gebruik kan word as 'n voorlopige gids om die gedrag van kobalt in silika-versadigde slakke tydens karbotermiese reduksie te verstaan. Kobalt herwinnings was oor die algemeen hoër il) die plasmaboogoond as vir die ooreenstemmende reaksies in die buisoond. Daar het egter beduidende hoeveelhede silikon en koolstof In die legering opgelos tydens die plasmaboogoond eksperimente.

Thesis (MScEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Ferrohydrostatic separation (FHS) of materials is a float and sink technique which utilizes ferrofluid exposed to a non-homogeneous magnetic field. The efficiency of material separation depends on numerous variables. The most important variables, which were investigated individually, are the effects of moisture content, ferrofluid level, feedrate, particle size and material density distribution on separation efficiency. It is important to recover and recycle the ferrofluid attached to the products of separation so as to reduce the cost of the FHS technology and the amount of kerosene disposed of to the environment. This prompted research into some of the factors affecting ferrofluid recovery. The factors that were investigated are the effects ofFHS operation, material moisture content, particle size and porosity. The separation efficiency was found to be dependent on all the variables investigated. The effect of material moisture content is less pronounced for particles larger than 2.8 mm. This implies that wet feed material should be screened before ferrohydrostatic separation and material which particle size is less than 2.8 mm should preferably be treated dry. Wet material (less than 2.8 mm) floats, even though its density is greater than the cut-point density. This is owing to the immiscibility of the water coating the particles and the kerosene-based ferrofluid used for separation. It was found that the effect of ferrofluid level on separation efficiency is a function of both the density difference of the particles to be separated and the particle size. Separation efficiency as a function of ferrofluid level is poor for particles larger than 2 mm and is good when the density difference of the material to be separated is high, for instance between 2700 kg/nr' and 3530 kg/nr'. This shows that for efficient separation of coarse particles and near density material (material with density close to the cut-point density), the ferrofluid level should be controlled, preferably close to the maximum possible level. The effect of feedrate on separation efficiency is also a function of the densities of the particles to be separated. An increase in feedrate leads to poor separation for particles with densities close t~ each other. This implies that separation of near density material requires accurate feedrate control. It has been shown from simulation and modelling that the effective cutpoint density changes as the particle moves through the chamber until it eventually reaches its terminal velocity, given that the chamber is of sufficient size for this to occur. The effective cut-point density increases to the maximum as the particle enters the ferrofluid pool but settles down to a relative constant once the particle has reached its terminal velocity. The effective cut-point density was shown to decrease with an increase in particle magnetisation. It was found that this decrease in the cut-point density determines the density difference (difference between two particles) achievable when non-magnetic material is treated together with magnetic material. It is therefore important to magnetically scalp the feed material for efficient separation. When the material is not scalped, magnetic and nonmagnetic material with the same density might report to different density fractions, which leads to poor separation. This magnetic contribution to the effective density can be utilised in the separation of material with same density but different magnetisation. The efficiency offerrofluid recovery was found to be dependent on all the variables investigated. The amount of ferrofluid drawn from the FHS separator was found to decrease with an increase in the magnetic field. Furthermore, the amount of ferrofluid that remains attached to the particles after allowing ferrofluid to drain from the material is the same as that attached to the FHS products of separation at high magnetic fields. This shows that it is important to operate the ferrohydrostatic separator at high magnetic fields in order to attract most of the ferrofluid back to the separator. T-heamount of ferrofluid adsorbed onto and absorbed by the particles was found to decrease with an increase in the material moisture content. This is due to two factors. The first is that water occupies the vacant pores in the material. The second is that water forms a layer on the particle surface which is immiscible with kerosene-based ferrofluid. This phenomenon leads to a reduction in cost of the ferrohydrostatic separation technology when wet material as opposed to dry material is treated. As already described coarse material larger than 2.8 mm can be treated wet without detrimental effects on separation. For -8+4 mm particles, the ferrofluid loss ranges from 0.6 down to 0.14 kg/tonne of feed for 0 to 10 % material moisture content respectively. The amount of ferrofluid lost per tonne of feed was found to range from 0.73 to 0.56 kg for-O.85+O.5 mm to -12+8 mm particle sizes respectively. The increase in ferrofluid loss in small particles is due to the increase in surface area in small particles for ferrofluid adsorption. The increase in porosity increases the amount of ferrofluid lost due to the difficulties in recovering ferrofluid embedded in the pores of the particles. Adding water to coarse material lowers the amount of ferrofluid lost by reducing porosity. Modelling the amount of ferrofluid lost, as a function of particle size and porosity, would assist in determining the amount of ferrofluid required to treat a known amount of material. The quality of ferrofluid recovered was found to be the same as that initially used for material separation. This implies that the separation efficiency would not be affected by the use of recycled ferrofluid. / AFRIKAANSE OPSOMMING: Ferro-hidrostatiese skeiding van materiale is 'n flotasie (dryf) en besinkingstegniek wat gebruik maak van ferro-vloeistof wat blootgestel is aan 'n magnetiese veld. Die effektiwiteit van die materiaal skeiding is afhanklik van verskeie veranderlikes. Die belangrikste veranderlikes wat die skeidingseffektiwiteit beïnvloed is individueel bestudeer, naamlik voginhoud, ferro-vloeistof vlak, voertempo, partikelgrootte en materiaal digtheid verspreiding. Dit is belangrik om die ferro-vloeistof te herwin en te hergebruik om die koste van die proses en tegnologie te verminder en dus ook die hoeveelheid keroseen wat aan die omgewing blootgestel is. Dit het navorsing tot gevolg gehad oor die faktore wat ferro-vloeistofherwinning beïnvloed. Hierdie.faktore wat ondersoek is in hierdie studie is materiaal voginhoud, partikelgrootte en porositeit. Die skeidingseffektiwiteit was afhanklik van al die faktore wat ondersoek is. Die effek van materiaal voginhoud was minder beduidend vir partikels groter as 2.8 mm. Dit wys dat nat voermateriaal moet gesif word voor ferro-hidrostatiese skeiding, en materiaal met 'n partikelgrootte kleiner as 2.8 mm moet verkieslik gedroog word. Nat materiaal (minder as 2.8 mm) floteer selfs as die digtheid groter is as die snypunt digtheid. Dit is as gevolg van ondeurlaatbaarheid van die water wat die partikels bedek en die keroseen basis ferro-vloeistofwat gebruik word vir die skeiding. Dit is gevind dat die invloed op die skeidingseffektiwiteit van die ferrovloeistof vlak is 'n funksie van beide die digtheid van die partikels wat geskei word. Die partikelgrootte skeidingseffektiwiteit as 'n funksie van die ferro-vloeistof vlak, is swak vir partikels groter as 2 mm en is goed wanneer die digtheid verskil van die materiaal wat geskei moet word, hoog is, byvoorbeeld 2 700 kg/nr' en 3 530 kg/nr'. Dit wys dat vir die effektiewe skeidings vir groter partikels en naby digtheid materiaal (materiaal net 'n digtheid nabyaan die snypunt digtheid), moet die ferro- . vloeistofvlak baie goed beheer word, gewoonlik naby die maksimum vlak moontlik. Die effek van voertempo op die effektitiwiteit van skeiding is ook 'n funksie van die digtheid van die partikels wat geskei moet word. 'n Toename in die vloeitempo lei tot 'n swak skeiding van partikels met digthede wat naby mekaar lê. Dit wys weer daarop dat die skeiding van naby digtheid materiaal het die akkurate beheer van voertempo tot gevolg. Dit is gevind deur simulasie en modulering dat die effektiewe snypuntdigtheid verander soos die partikel deur die kamer beweeg totdat dit uiteindelik sy finale snelheid bereik (gegee dat die kamer groot genoeg is). Dit effektiewe snypunt digtheid verhoog tot 'n maksimum wanneer die partikel die ferro-vloeistof binne gaan, maar bereik na 'n kort tydperk 'n kostante waarde sodra die partikel sy finale snelheid bereik het. Die effektiewe snypunt digtheid verlaag met 'n toename in partikel magnetisme. Dit is gevind dat die afname in die snypunt digtheid bepaal die digtheidsverskil (verskil tussen twee partikels) wat bereikbaar is wanneer nie-magnetiese materiaal saam met magnetiese materiaal behandel word. Dit is dus belangrik om die voer materiaal magneties te skalpeer vir effektiewe skeiding. Wanneer die materiaal so behandel word, sal magnetiese en nie-magnetiese materiaal, met die dieselfde digthede, rapporteer in verskillende digtheidsfraksies wat sal lei tot swak skeiding. Die magnetiese bydrae tot die effektiewe digtheid kan gebruik word in die skeiding van materiaal met dieselfde digtheid, maar met verskillende magnetismes. Die effektiwiteit van ferro-vloeistof herwinning is afhanklik van al die veranderlikes wat ondersoek is. Die hoeveelheid ferro-vloeistof wat omtrek is van die ferro-hidrostatiese skeier verminder met 'n toename in die magnetiese veld. Verder is die ferro-vloeistof wat agterbly as gevolg van die feit dat hulle vas is aan die partikels na dreinering, dieselfde as die hoeveelheid wat vasgeheg is aan die die ferro-hidrostatisiese produkte van skeiding by hoë magnetiese velde. Dus is dit belangrik om die ferrohidrostatiese skeier te bedryf by hoë magnetiese velde om sodoende die meerderheid van die ferro-vloeistof in die skeier agter te laat bly. Die hoeveelheid ferro-vloeistof geadsorbeer aan en geabsorbeer deur die partikels verlaag met 'n toename in die materiaal voginhoud. Dit is gevolg van twee redes, nl. eerstens water wat die plek inneem van die oop porieë in die materiaal, en tweede is die feit dat water 'n lagie op die partikeloppervlakte vorm wat ondeurlaatbaar is vir keroseen-basis ferrovloeistof Dit lei tot die vermindering in koste van die ferro-hidrostatiese skeidingstegnologie wanneer nat materiaal in plaas van droë materiaal gebruik word. Soos alreeds genoem, partikels groter as 2.8 mm kan nat behandel word sonder enige negatiewe effekte op die skeiding. Vir -8+4 mm partikels is daar 'n ferro-vloeistofverlies van 0.6 tot 0.14 kg/ton voer vir' n 0-10% voginhoud. Die hoeveelheid ferro-vloeistof per ton voer materiaal wat verlore gaan wissel tussen 0.73 tot 0.56 kg vir -0.85+0.5 mm tot -12+8 mm partikelgroottes, respektiewelik. Die toename in ferro-vloeistofverlies by kleiner partikels is as gevolg van die toename in die oppervlakarea van kleinpartikels vir ferro-vloeistof adsorpsie. Daar is 'n toename in porositeit wat gepaard gaan met 'n toename in hoeveelheid in ferro-vloeistof wat verlore gaan as gevolg van probleme met die herwinning van ferro-vloeistof wat binne-in partikelporieë vasgevang IS. Die byvoeging van water by groter materiaal verlaag die hoeveelheid . ferro-vloeistofwat verlore gaan as gevolg van verminderde porositeit. Die modellering van die hoeveelheid ferro-vloeistof wat verlore gaan, as 'n funksie van die partikelgrootte en porositeit, sal help met die skatting van die hoeveelheid ferro-vloeistof benodig om 'n sekere hoeveelheid materiaal te behandel. Dit is gevind dat die kwaliteit van die ferro-vloeistof wat herwin word dieselfde is as die wat aanvanklik gebruik is vir die materiaal skeiding. Dit wys dat die skeidingseffektiwiteit beïnvloed nie die gebruik van gehersirkuleerde ferro-vloeistof nie.

Thesis (MScEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Inorganic membranes offer numerous advantages, such as stability at high temperatures and a long lifetime. Two Russian professors invented and patented a method for manufacturing a tubular ceramic membrane [Linkov & Belyakov, 1996]. Their membranes were used in the water purification industry and in gas separation research at the University of Stellenbosch [Keuier, 2000], but the performance of the membranes have been reported to be inconsistent. This project investigates the manufacturing process for these membranes in an attempt to improve their inconsistent performance. It also provides useful insight into relevant methods of evaluation. Thirty-two cerarruc membranes were successfully manufactured according to the patent by Linkov and Belyakov [1996], with slight modifications to the original manufacturing process. It was found for example that, to obtain membranes with a thickness of 1 mm, the casting suspension should contain 1.85 grams of water per gram of oxides, instead of the 1.15 grams of water per gram of oxides according to Linkov and Belyakov [1996]. The quality of the gypsum mould and the drying of the green body were found to be the most difficult steps in the manufacturing process. Gas permeabilities for the manufactured membranes were typically lxIO-5 mol/misl'a for argon and nitrogen and 4.SxIO-5 mol/rrr'sl'a for hydrogen. Water permeabilities for the manufactured membranes were typically 600 Vm2hbar. Gas permeability coefficients for the manufactured membranes were typically SxIO-15 m2 for nitrogen and argon and 8xIO-15 m2 for hydrogen. The water permeability coefficients were typically 1.7xl 0-15 m2 . The gas and water permeabilities for the manufactured membranes were typically 5 and 10 times higher than the permeability values for membranes manufactured by Linkov. Gas and liquid permeability coefficients for the manufactured membranes, taking into account the thickness of the membranes, were 7 and 14 times higher than those achieved with Linkov's membranes. Linkov's membranes were on average thinner than the manufactured membranes, while the permeability of the manufactured membranes was higher, explaining the high permeability coefficients. The nitrogen and argon permeabilities, as well as their permeability coefficients were found to increase linearly with increasing pressure difference. However, the hydrogen permeability and permeability coefficients as well as the water permeability coefficients, were pressure independent. The gas permeability results also indicated that the permeability of the manufactured membranes increased with increasing sintering time and temperature. Combining the gas permeability results with the selectivity results, manufactured membranes with higher gas permeability had the same selectivity as Linkov's membrane. Therefore the manufactured membranes had a higher capacity than Linkov's membranes, with the same selectivity. For the manufactured membranes, however, a lower mechanical strength was reported, typically 9 N/mm2 , compared to the mechanical strength of Linkov's membrane which was roughly 10 times higher. To further improve the membranes, a number of options can be investigated: • The influence of a higher zirconia content on the ceramic membranes (between 29W'1o and 36.6W'1o for best mechanical strength). • Increasing of the sintering time and temperature for a more sintered and mechanically stronger membrane. • Examining the relationship between the permeability and mechanical strength of the membranes. / AFRIKAANSE OPSOMMING: Anorganiese membrane besit 'n aantal voordele, soos stabiliteit by hoë temperatuur toepassings en 'n langer leeftyd. Twee Russiese professore het 'n vervaardigingsmethode vir buisvormige keramiekmembrane uitgevind en gepatenteer [Linkovand Belyakov, 1996]. Hulle membrane was gebruik in die watersuiwerings industrie sowel as in 'n gasskeidings ondersoek by die Universiteit van Stellenbosch [Keuier, 2000], maar die prestasie van die membrane was wisselvallig. Hierdie projek ondersoek die vervaardigings metode vir hierdie kerarniekmembrane in 'n poging die wisselvallige prestasie van die membrane te verbeter. Die projek gee ook bruikbare insig in relevante toetsmetodes vir die vervaardigde membrane. Twee en dertig keramiekmembrane was suksesvol vervaardig volgens die patent van Linkoven Belyakov [1996], met klein veranderings. Dit was byvoorbeeld gevind dat, om membrane te vervaardig met 'n dikte van 1 mm, die gietsuspensie 1.85 gram water per gram oxide moet bevat in plaas van een gram water per een gram oxides soos volgens Linkoven Belyakov [1996]. Die kwaliteit van die gips vorm en die droog van die groen liggaam was die moeilikste beheerbare stappe in die vervaardigingsproses. Die gasdeurlaatbaarheid van die vervaardigde membrane was tipies Ix 10-5 mollm2sPa vir argon en stikstof en 4.5xl0-s mol/m'sl'a vir waterstof Waterdeurlaatbaarheid van die vervaardigde membrane was 600 l/rrr'hbar. Gasdeurlaatbaarheidskoeffisiente vir die vervaardigde membrane was tipies 5xl 0-15 m2 vir argon en stikstof en 8xl 0-15 m2 vir waterstof Die waterdeurdringbaarheidskoeffisiente was tipies 1.7xl 0-15 m2 . Die gas- en waterdeurlaatbaarheid vir die vervaardigde membrane was tipies 5 en 10 maal hoër as die deurlaatbaarheid waardes vir membrane wat deur Linkov vervaardig is. Gas- en waterdeurlaatbaarheidskoeffisiente vir die vervaardigde membrane, wat deur die dikte van die membrane beinvloed word, was 7 en 14 maal hoër as die bereik met Linkov se membrane. Linkov se membrane was gemiddeld dunner as die vervaardigde membrane, terwyl die deurlaatbaarheid van die vervaardigde membrane hoër was, wat die hoë deurlaatbaarheidskoeffisiente verklaar. Daar was gevind dat die argon- en stikstofdeurlaatbaarhede sowel as hulle deurlaatbaarheidskoeffisiente lineêr toeneem met toenemende drukverskil. Die waterstofdeurlaatbaarheid en -deurlaatbaarheidskoeffisiente sowel as die waterdeurlaatbaarheidskoeffisiente egter, was onafhanklik van die drukverskil. Die gasdeurlaatbaarheid resultate het ook aangedui dat die deurlaatbaarheid van die vervaardigde membrane toeneem met toenemende sintertyd en -ternperatuur. Wanneer die gasdeurlaatbaarheid resultate gekombineer word met die selektiwiteit resultate blyk dit dat, terwyl dat die vervaardigde membrane 'n hoër gasdeurlaatbaarheid het as Linkov se membrane, hulle nog steeds dieselfde selektiwiteit het. Dit beteken dat die kapasiteit van die vervaardigde membrane hoër is, terwyl die selektiwiteit van die skeidingsproses behou word. Vir die vervaardigde membrane was 'n laer meganiese sterkte gevind, tipies 9 N/mm2 , terwyl die meganiese sterkte van Linkov se membrane omtrend 10keer hoër was. Verskeie opsies kan ondersoek word om die membrane te verbeter: • Die invloed van 'n hoër zirkonia inhoud op die keramiekmembrane (tussen 29m% en 36.6m% vir beste meganiese sterkte). • Verlenging van die sintertyd en -temperatuur om 'n meer gesinterde en meganies sterker keramiekmembraan te verkry. • Ondersoek na die verhouding tussen deurlaatbaarheid en die sterkte van die membraan.

Thesis (MScEng) -- Stellenbosch University , 2002. / ENGLISH ABSTRACT: The distillation process is the most widely used separating process in the chemical process industry. The optimal design of the distillation units can lead to reduced capital costs and improved energy utilisation. This is particularly the case for structured packed distillation column where design methods tend to over-predict the column efficiency. This work seeks to contribute to the development of a reliable mass transfer model for structured packing. A gas phase mass transfer correlation was developed based on the evaporation of pure components into an air stream. The mass transfer rates were measured in a short triangular wetted wall channel with a corrugated surface wall. The influence that the geometric configuration as well as surface structure has on the mass transfer rates was investigated. The channel geometry and surface wall structure resembled that of the structured packing (Flexipac 350Y). The influence of the channel geometry on the gas mass transfer rates was not significant except at low flow conditions. The liquid phase resistance was investigated for binary mixtures in the triangular wetted wall channel. It was found that the overall mass transfer rate decreased with increasing composition of the volatile component. The enhancement of the gas phase mass transfer rate masked the presence of the liquid resistance. ii The gas phase mass transfer correlations were used in the mass transfer model to predict the separation efficiency of a structured packed distillation column. The structured packing used to validate the mass transfer model was high-capacity Flexipac 350Y and normal Flexipac 350Y. The binary distillation experiments were done at total reflux conditions for the pressure range O.33-1atm. The accuracy of the separation efficiencies of the mass transfer model improved with increasing pressure for both materials. The mass transfer model was able to predict the variation of separation efficiencies with column loadings. / AFRIKAANSE OPSOMMING: Distillasie is die skeidingsmetode wat die meeste in die chemiese industrie gebruik word. Die optimale ontwerp van distillasie eenhede kan lei tot verlagings in kapitaalkostes en 'n verbeterde gebruik van energie. Dit is veral waar in die geval van kolomme met gestruktureerde pakking waar huidige ontwerpsmetodes, die kolomeffektiwiteit nie akkuraat beskryf nie. Hierdie studie het ten doelom 'n bydrae te lewer tot die ontwikkeling van 'n betroubare massa-oordragsmodel vir gestruktureerde pakking. 'n Gasfase massa-oordragskorrelasie is ontwikkel gebaseer op metings van die verdampingstempo van suiwer komponente in 'n lugstroom. Die massaoordragstempos is gemeet in 'n kort driehoekige benatle wand kanaal waarin die wand 'n bepaalde oppervlakprofiel het. Die invloed van beide die kanaalgeometrie en die oppervlakprofiel is ondersoek. Die geometrie en oppervlakprofiel is soorgelyk aan die van Flexipac 350Y gestruktureerde pakking. Die invloed van die kanaalgeometrie op die gasfase massaoordragstempos is slegs beduidend by lae vloeitempos. Die vloeistoffase weerstand vir binêre mengsels is ondersoek in die driehoekige kanaal. Dit is gevind dat die algehele massa-oordragstempo verlaag met 'n verhoging in die konsentrasie van die vlugtige komponent. Die verhoging in die gasfase massa-oordragstempo verberg die invloed van die vloeistoffase weerstand. Die gasfase massa-oordragskorrelasies is in 'n massa-oordragsmodel gebruik om die skeidingseffektiwiteit van gestruktureerde pakking in "n kolom te voorspel. Metings op hoë-kapasiteit Flexipac 350Y en normale Flexipac 350Y is gebruik om die modelvoorspellings te evalueer. Die binêre distillasies is by totale terugvloei gedoen in die drukbereik 0.33 - 1.0 atm. Daar is gevind dat die model meer akkuraat is by hoër drukke. Die massa-oordragsmodel is in staat om die variasie in skeidingseffektiwiteit met veranderende kolomlading te voorspel.

Thesis (MScEng)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Slag foaming occurs in several pyrometallurgical processes. These processes include steelmaking in basic oxygen steelmaking furnaces and electric arc furnaces (EAF) as well as various non-ferrous operations like sulphide smelting/converting and base metal slag cleaning. Although slag foaming in steelmaking processes has been extensively researched, little attention has been given to slag foaming in non-ferrous operations. Slag foaming phenomena are complex because often the system consists of three or more phases. The objectives of this study is to review the published work on slag foaming, to obtain through physical modelling an understanding of the principles governing foaming and to investigate slag foaming phenomena through pyrometallurgical experiments. To obtain these objectives, experiments were carried out with aqueous mixtures at different column sizes, different pore sizes for gas injection and varying liquid depths, and also for high temperature metallurgical slags with varying composition and at different temperatures. Through gas injection, foaming conditions were simulated and the equilibrium foam height was measured for different gas velocities. The following conclusions were drawn: 1. For physical modelling of slag foaming in 3-phase systems the average foam index increases with increasing amounts of solids present in the system. The effect of additional solids in the system is independent of the system geometry. 2. The following conclusions were reached by determining coefficients for an empirical dimensional model fitted to aqueous mixtures: Higher liquid density leads to lower foam index values. The influence of the liquid viscosity is dependent on the system investigated and may have a positive or negative result on foaming. The empirical model should only be applied to the property range and geometric set-up for which it was derived, as coefficients may vary greatly for different systems. 3. Influence of solid precipitates on slag foaming can be summarised by noting that small amounts of magnetite stabilise slag foaming, while precipitates of wollastonite and anorthite decreased foaming. The influence of solid precipitates is thought to be related to the density, morphology and degree of surface activity of the solid precipitates. 4. The foam index decreases with increasing basicity due to the lowering of the slag viscosity. This continues until the precipitation of solids starts and the foam index once again increases. 5. For increasing "FeO" concentration the foam index will decrease due to lower viscosity, but higher surface tension depression may lead to increased foam index values at high "FeO" concentrations. 6. Higher foam index values were obtained for slags with lower densities. The _1 empirical relationship observed is L IX: P 3 . 7. Higher foam index values were obtained for slags with higher viscosity. The empirical relationship observed is L IX: f1 . 8. Higher foam index values were obtained for slags with lower surface tensions. The empirical relationship observed is L IX: U-I. 9. Models derived for the foaming of basic steelmaking slags does not satisfactorily describe the foaming behaviour of acidic slags. 10. The physical properties of the slag influence the foam stabilisation mechanism. / AFRIKAANSE OPSOMMING: Slak skuiming kom in verskeie pirometallurgiese prosesse voor. Hierdie prosesse sluit die maak van staal in basiese staalmaakoonde en elektriese boogoonde in, sowel as verskeie nie-yster prosesse soos sulfied smelting/omsetting en die skoonmaak van basis metaal slakke. Alhoewel slak skuiming in staalmaak slakke reeds intensief nagevors is, is min aandag gegee aan slak skuiming in nie-yster prosesse. Slak skuiming verskynsels is kompleks, want dikwels betaan die sisteem uit drie of meer fases. Die doelwitte van hierdie studie is om werk wat reeds oor slakskuiming gepubliseer is te hersien, om deur fisiese modellering 'n begrip van die prinsiepe waarop skuiming berus te bekom en om slak skuiming verskynsels na te vors deur piromettallurgiese eksperimente te beplan en uit te voer. Ten einde hierdie doelwitte te bereik, is eksperimente uitgevoer met water mengsels in verskillende kolom groottes, verskillende porie groottes vir gas inspuiting en by verskillende vloeistof hoogtes, en ook vir hoë temperatuur metallurgiese slakke met variërende samestelling en by verskillende temperature. Skuimingskondisies is deur gas inspuiting gesimuleer en die ewewig skuimhoogte is gemeet by verskillende gas snelhede. Die volgende gevolgtrekkings is bereik: 1. Tydens fisiese (koue) modellering van slak skuiming in 3-fase sisteme styg die gemiddelde skuim indeks met toenemende hoeveelhede vastestof in die sisteem. Die uitwerking van addisionele vastestof in die sisteem is onafhanklik van die sisteem geometrie. 2. Die volgende gevolgtrekkings is gemaak deur die koëffisiente vir 'n empiriese dimensionale model te pas op waterige mengsels. Hoër vloeistof digtheid lei na laer skuim indeks waardes. Die invloed van die vloeistof viskositeit is afhanklik van die sisteem ondersoek en mag 'n positiewe of 'n negatiewe resultaat op skuiming hê. Die empiriese model moet slegs toegepas word op die eienskap omvang en geometriese opstelling waarvoor dit bepaal is, omdat koëffisiënte grootliks kan varieer vir verskillende sisteme. 3. Die invloed van vastestof partikels op slak skuiming kan opgesom word deur die waarneming dat klein hoeveelhede magnetiet slakskuiming stabiliseer terwyl neerslag van wollastoniet en anhortiet skuiming verminder. Die invloed van vastestof neerslag hou vermoedelik verband met die digtheid, vorm en graad van oppervlak aktiviteit van die vastestof partikels. 4. Die skuim indeks verminder met toenemende basisiteit as gevolg van die afname in die slak viskositeit. Dit geld tot die neerslag van vastestof begin en die skuim indeks weereens toeneem. 5. Vir toenemende 'FeO' konsentrasie sal die skuim indeks afneem as gevolg van laer viskositeit, maar hoër oppervlakspanning onderdrukking kan lei na hoër skuim indeks waardes by hoër 'FeO' konsentrasies. 6. Hoër skuim indeks waardes is verkry vir slakke met laer digthede. Die empiriese _1 verhouding is bepaal as L cx: p 3 . 7. Hoër skuim indeks waardes is verkry vir slakke met hoër viskositeit. Die empiriese verhouding is bepaal as L cx: Jl . 8. Hoër skuim indeks waardes is verkry vir slakke met laer oppervlakspannings. Die empiriese verhouding is bepaal as L cx: 0--1 • 9. Modelle afgelei vir die skuiming van basiese staalmaak slakke beskryf nie die skuimings gedrag van suur slakke bevredigend nie. 10. Die fisiese eienskappe van die slak beïnvloed die skuim stabiliseerings meganisme.

Thesis (MScEng)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Flotation is notorious for its susceptibility to process upsets and consequently its poor performance, making successful flotation control systems an elusive goal. The control of industrial flotation plants is often based en the visual appearance of the froth phase, and depends to a large extent on the experience and ability of a human operator. Machine vision systems provide a novel solution to several of the problems encountered in conventional flotation systems for monitoring and control. The rapid development in computer VISIon, computational resources and artificial intelligence and the integration of these technologies are creating new possibilities in the design and implementation of commercial machine vision systems for the monitoring and control of flotation plants. Current machine vision systems are available but not without their shortcomings. These systems cannot deal with fine froths where the bubbles are very small due to the segmentation techniques employed by them. These segmentation techniques are cumbersome and computationally expensive making them slow in real time operation. The approach followed in this work uses neural networks to solve the problems mentioned above. Neural networks are able to extract information from images of the froth phase without regard to the type and structure of the froth. The parallel processing capability of neural networks, ease of implementation and the advantages of supervised or unsupervised training of neural networks make them potentially suited for real-time industrial machine vision systems. In principle, neural network models can be implemented in an adaptive manner, so that changes in the characteristics of processes are taken into account. This work documents the development of linear and non-linear principal component models, which can be used in a real-time machine vision system for the monitoring, and control of froth flotation systems. Features from froth images of flotation processes were extracted via linear and non-linear principal component analysis. Conventional linear principal component analysis and three layer autoassociative neural networks were used in the extraction of linear principal components from froth images. Non-linear principal components were extracted from froth images by a three and five layer autoassociative neural network, as well as localised principal component analysis based on k-means clustering. Three principal components were extracted for each image. The correlation coefficient was used as a measure of the amount of variance captured by each principal component. The principal components were used to classify the froth images. A probabilistic neural network and a feedforward neural network classifier were developed for the classification of the froth images. Multivariate statistical process control models were developed using the linear and non-linear principal component models. Hotellings T2 statistic and the squared prediction error based on linear and non-linear principal component models were used in the development of multivariate control charts. It was found that the first three features extracted with autoassociative neural networks were able to capture more variance in froth images than conventional linear principal components, the features extracted by the five layer autoassociative neural networks were able to classify froth images more accurately than features extracted by conventional linear principal component analysis and three layer autoassociative neural networks. As applied, localised principal component analysis proved to be ineffective, owing to difficulties with the clustering of the high dimensional image data. Finally the use of multivariate statistical process control models to detect deviations from normal plant operations are discussed and it is shown that Hotellings T2 and squared prediction error control charts are able to clearly identify non-conforming plant behaviour. / AFRIKAANSE OPSOMMING: Flottasie is berug daarvoor dat dit vatbaar vir prosesversteurings is en daarom dikwels nie na wense presteer nie. Suksesvolle flottasiebeheerstelsels bly steeds 'n ontwykende doelwit. Die beheer van nywerheidsflottasie-aanlegte word dikwels gebaseer op die visuele voorkoms van die skuimfase en hang tot 'n groot mate af van die ervaring en vaardighede van die menslike operateur. Masjienvisiestelsels voorsien 'n vindingryke oplossing tot verskeie van die probleme wat voorkom by konvensionele flottasiestelsels ten opsigte van monitering en beheer. Die vinnige ontwikkeling van rekenaarbeheerde visie, rekenaarverwante hulpbronne en kunsmatige intelligensie, asook die integrasie van hierdie tegnologieë, skep nuwe moontlikhede in die ontwerp en inwerkingstelling van kommersiële masjienvisiestelsels om flottasie-aanlegte te monitor en te beheer. Huidige masjienvisiestelsels is wel beskikbaar, maar is nie sonder tekortkominge nie. Hierdie stelsels kan nie fyn skuim hanteer nie, waar die borreltjies baie klein is as gevolg van die segmentasietegnieke wat hulle aanwend. Hierdie segmentasietegnieke is omslagtig en rekenaargesproke duur, wat veroorsaak dat dit stadig in reële tyd-aanwendings is. Die benadering wat in hierdie werk gevolg is, wend neurale netwerke aan om die bovermelde probleme op te los. Neurale netwerke is instaat om inligting te onttrek uit beelde van die skuimfase sonder om ag te slaan op die tipe en struktuur van die skuim. Die parallelle prosesseringsvermoëns van neurale netwerke, die gemak van implementering en die voordele van die opleiding van neurale netwerke met of sonder toesig maak hulle potensieel nuttig as reële tydverwante industriële masjienvisiestelsels. In beginsel kan neurale netwerke op 'n aanpassende wyse geïmplementeer word, sodat veranderinge in die kenmerke van die prosesse deurlopend in aanmerking geneem word. Kenmerke van die beelde van die skuim tydens die flottasieproses is verkry by wyse van lineêre en nie-lineêre hootkomponentsanalise. Konvensionele lineêre hoofkomponentsanalise en drie-laag outo-assosiatiewe neurale netwerke is gebruik in die onttrekking van lineêre hoofkomponente uit die beelde van die skuim. Nie-lineêre hoofkomponente is uit die beelde van die skuim onttrek by wyse van 'n drie- en vyf-laag outo-assosiatiewe neurale netwerk, asook deur 'n gelokaliseerde hoofkomponentsanalise wat op k-gemiddelde trosanalise gebaseer is. Drie hoofkomponente is vir elke beeld onttrek. Die korrelasiekoëffisiënt is gebruik as 'n maatstaf van die afwyking wat deur elke hoofkomponent aangetoon is. Die hoofkomponente is gebruik om die beelde van die skuim te klassifiseer. 'n Probalistiese neurale netwerk en 'n voorwaarts voerende neurale netwerk is vir die klassifisering van die beelde van die skuim ontwerp. Multiveranderlike statistiese prosesbeheermodelle is ontwerp met die gebruik van die lineêre en nie-lineêre hoofkomponentmodelle. Hotelling se T2 statistiek en die gekwadreerde voorspellingsfout, gebaseer op lineêre en nie-lineêre hoofkomponentmodelle, is gebruik in die ontwikkeling van multiveranderlike kontrolekaarte. Dit is gevind dat die eerste drie eienskappe wat met behulp van die outo-assosiatiewe neurale netwerke onttrek is, instaat was om meer variansie by beelde van skuim vas te vang as konvensionele lineêre hoofkomponente. Die eienskappe wat deur die vyf-laag outo-assosiatiewe neurale netwerke onttrek is, was instaat om beelde van skuim akkurater te klassifiseer as daardie eienskappe wat by wyse van konvensionele lineêre hoofkomponentanalalise en drie-laag outo-assosiatiewe neurale netwerke onttrek is. Soos toegepas, het dit geblyk dat gelokaliseerde hoofkomponentsanalise nie effektief is nie, as gevolg van die probleme rondom die trosanalise van die hoë-dimensionele beelddata. Laastens word die aanwending van multiveranderlike statistiese prosesbeheermodelle, om afwykings in normale aanlegoperasies op te spoor, bespreek. Dit word aangetoon dat Hotelling se T2 statistiek en gekwadreerdevoorspellingsfoutbeheerkaarte instaat is om afwykende aanlegwerksverrigting duidelik aan te dui.

Thesis (MScEng)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Desired behaviour of paint during processing, storage, application and after application is of great importance in the coatings industry. Rheology (the study of flow and deformation behaviour) is used as a method to investigate the behaviour of the flow and deformation properties of the paint during these stages. Some of the more important phenomena that can occur during these stages, which were examined rheologically, are: 1. The rheological behaviour of certain complex raw materials during processing - vesiculated beads suspensions 11. The paint behaviour during storage - in-can stability, e.g. phase separation and sedimentation of particles; Ill. The paint during application - ease of application, spatter, etc.; IV. The paint behaviour after application - sag, layer thickness, levelling (ability to hide brush marks), etc. A rheometer was used to obtain rheological curves from a paint sample (± 1 ml). Correct interpretation of these curves, which display rheological properties of the sample such as the viscosity, shear stress, structural strength and many more, produced information about the properties mentioned in i, ii, iii and iv above. It was found that the rheological data correlated well with empirical tests carried out in the laboratory for spatter, sag, levelling behaviour and in-can stability of the paint. A wide variety of paints were studied ranging from tough/durable outdoor paints to smooth/velvety indoor paints. The rheological behaviour explained the specific end-use properties of the paints. Paints from two different companies were compared on a rheological basis. In some cases large differences in rheological behaviour were observed. Rheology modifiers were tested on a new paint. It was found that specific rheology modifiers could be incorporated into the formulation to give the specific rheological behaviour required. Rheological modelling was performed and it was found that the flow behaviour of paint cou1d be modelled accurately with existing viscosity models (Ostwald/de Waal, Bingham, Casson, Herschel-Bulkley, Cross and Philips-Deutsch). Other rheological properties of paint were also modelled successfully with a simple linear regression model. Rheology was also used as a method to examine the flow and deformation properties of vesiculated beads, a component of paint with very complex rheology. The most important factors that influence the rheological behaviour of the vesiculated beads were determined. It was found that the type of manufacturing process for the beads affected the rheological behaviour. The effect of the raw materials used to manufacture the vesiculated beads were rheologically determined. / AFRIKAANSE OPSOMMING: Dit is baie belangrik dat verf die gewenste gedrag moet toon tydens berging, vervaardiging, tydens aanwending en direk na aanwending. Reologie (die studie van vloei- en vervorming) word gebruik as a metode om die vloei- en vervormingseienskappe van verf gedurende bogenoemde stadia te ondersoek. Sommige van die belangriker verskynsels wat gedurende hierdie stadia kan plaasvind, is d.m.v reologiese toetse ondersoek. Die verskynsels is as volg: i. Die reologiese gedrag van komplekse grondstowwe soos gevesikuleerde partikel suspensies. ll. Verfgedrag tydens berging - stabiliteit van verf in die blik, bv. faseskeiding en sedimentasie van partikels lll. Verfgedrag tydens aanwending - gemak van aanwending, spatsels IV. Verfgedrag direk na aanwending - afsakking, dikte van verflaag, vloei-eienskappe 'n Reometer is gebruik om die reologiese kurwes te bepaal deur gebruik te maak van ± 1 ml monster. Korrekte interpretasie van hierdie kurwes, wat onder meer eienskappe soos viskositeit, spanning en struktuursterkte insluit, lei tot inligting wat die verskynsels in i, ii, iii en iv kan verklaar. Daar is gevind dat inligting wat verkry is i.v.m die verskynsel van spatsels, afsakking, vloei en die stabiliteit van verf in die blik, goed korreleer met empiriese toetse wat in die laboratorium uitgevoer is. 'n Groot verskeidenheid van verwe, wat wissel van duursame/sterk buitemuurse verf, tot fluweelsagte binnenshuise verf, isondersoek. Die reologiese toetse het daarin geslaag om die eienskappe van die eindproduk suksesvol te verduidelik. Verf van twee verskillende maatskappye is ook met mekaar vergelyk op 'n reologiese grondslag. Daar is by sommige van die verwe aansienlike verskille in die reologiese gedrag gevind. 'n Nuwe verf is gebruik om die uitwerking van reologie modifiseerders te ondersoek. Daar is gevind dat daar spesifieke reologie modifiseerders bestaan wat unieke reologiese gedrag verseker. Reologiese modellering is gedoen op verf en daar is gevind dat die vloeigedrag van die verf akkuraat gemodelleer kan word deur van die bestaande viskositeitsmodelle gebruik te maak (Ostwald/de Waal, Bingham, Casson, Herschel- Bulkley, Cross en Philips-Deutsch). Ander reologiese eienskappe is gemodelleer deur gebruik te maak van eenvoudige regressie modelle. Daar is ook van reologiese tegnieke gebruik gemaak om die vloei en vervormingseienskappe van gesuspendeerde gevesikuleerde partikels, wat as 'n grondstof vir verf gebruik word, te ondersoek. Die belangrikste faktore wat die reologiese gedrag beïnvloed het, was onder meer die verskillende prosesse waarmee die gevesikuleerde partikels vervaardig is. Die effek van sekere van die grondstowwe wat gebruik word om die gevesikuleerde partikels te vervaardig, is ook reologies ondersoek.

Thesis (MScEng)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: ABSTRACT: A new emulsion (code name: NW 120) has been developed by Plascon on laboratory scale, for application in the paint industry. It is an environmentally friendly emulsion in which no coalescent solvent is used. It also has a core-shell morphology. Research was undertaken to scale-up (industrialize) the emulsion polymerization of NW 120. The use of a suitable pilot plant was investigated. An available bench-scale pilot plant (RCl, Mettler Toledo) was found to be very expensive. The reactors were very small (R:1.8 l) and the reactor set-ups (reactor, baffies and stirrer configuration) were not similar to the industrial size reactors used by Plascon. A fully computer controlled bench-scale pilot plant was subsequently designed and built at a fraction of the cost of the commercially available set-up. The reactor (5 I) was a scale-down replica (geometrically similar) of the industrial size reactors used by Plascon. The reactor was designed to also serve as a calorimeter. Very good control was achieved over the reaction temperature and addition rates of the monomers and catalyst. Heat loss and heat capacity models were derived for a variation in the reaction temperature between 82.5 - 87.5 °c in order to perform accurate energy balances (calorimeter) around the reactor. The accuracy of the calorimeter was verified at a reaction temperature of 85°C, by measuring the heat that evolved when a sodium hydroxide solution was diluted with water. The accuracy of the calorimeter was found to be extremely good. The pilot plant was commissioned with an industrially manufactured emulsion (code name: AE 446), well known to Plascon. The results obtained in the pilot plant reactor were very similar to those obtained for the full-scale manufacturing of AE 446. It was determined that if geometrical similarity between the pilot plant reactor and the industrial size reactor is preserved and if the correct process conditions (stirring speed, reaction temperature and addition rates of the monomers/catalyst) are maintained, then the direct scale-up of the production ofNW 120, from bench-scale to full-scale, would be possible. The reaction conditions were varied over a wide range, in order to find the optimum process conditions. The stirring speed was varied between 150 - 550 rpm. Shear sensitivity was observed at stirring speeds of 450 rpm and higher. The measured physical properties at 550 rpm were found to be unacceptable. The optimum stirring speed for the desired particle size and viscosity was found to lie between 150 rpm and 250 rpm. The reaction temperature was varied between 70 and 90 DC. The optimum reaction temperature was found to lie between 80 and 90 De. It was possible to successfully reduce the monomer addition time, and hence the reaction times, by increasing the addition rate of the monomers/catalyst, from 4 h to 2 ~ h. The method developed by Klein et al. (1996), for the scale-up of the stirring speed of emulsion polymerization reactions was used to determine the equivalent fullscale stirring speed. The scale-up of NW 120 was subsequently conducted at 85 DC, at a stirring speed of 35 rpm and the monomers/catalyst were added over a period of 4 h. The use of reduced reaction times were not considered in the first scale-up run since at that stage it was not clear whether the heat removal capability of the industrial size reactor would be adequate to cope with the increase in the evolved heat, associated with an increase in the addition rates of the monomers/catalyst. Very good results were obtained. The measured physical properties of NW 120 produced in the industrial size reactor were found to be almost exactly the same as in the pilot plant reactor. / AFRIKAANSE OPSOMMING: 'n Nuwe emulsie (kode naam NW 120) is deur Plascon op laboratorium skaal ontwikkel, vir die gebruik in die verfbedryf. Dit is 'n omgewingsvriendelike produk en geen oplosmiddels word gebruik vir die filmvormingsproses nie. Hierdie projek handeloor die opskalering (industrialisering) van die produksie van NW 120. Die gebruik van 'n geskikte loodsaanleg is eers ondersoek. Daar is gevind dat die beskikbare laboratorium skaalloodsaanleg (RCl, Mettler Toledo) baie duur was. Die reaktore is baie klein (:::::1.81). Die reaktoropstellings (reaktor, keerplate en roerder-konfigurasie) is ook nie in ooreenstemming met die industriële grootte reaktore wat deur Plascon gebruik word nie. 'n Ten volle rekenaarbeheerde loodsaanleg is ontwerp en gebou teen 'n breuk van die koste van soortgelyke kommersieel beskikbare opstellings. Die reaktor (5 I) is 'n skaalmodel (geometries gelykvormig) van die industriële grootte reaktore wat deur Plascon gebruik word. Die reaktor word ook aangewend as 'n kalorimeter. Baie goeie beheer oor die reaktortemperatuur, sowel as die toevoertempo's van die monomere en die katalis is verkry. Hitteverlies en hittekapasiteits modelle is afgelei vir variasies in die reaktortemperatuur tussen 82.5 - 87.5 °c om dit moontlik te maak om akkurate energiebalanse te kan opstel (kalorimeter). Die akkuraatheid van die kalorimeter is getoets by 85°C, deur die verdunningswarmte van 'n natriumhidroksiedoplossing te meet. Daar is gevind dat die kalorimeter baie akkuraat is. 'n Industrieel vervaardigde (plaseon) emulsie (kode naam: AB 446) is gebruik om die loodsaanleg in bedryf te stel. Die resultate wat in die loodsaanleg verkry is, was ongeveer dieselfde as die resultate wat in die industriële reaktore verkry word. Hierdie resultate toon dat indien die reaktore geometries gelykvormig is en indien die regte prosestoestande (roerspoed, reaksietemperatuur en toevoertempo's van die monomere/katalis) gebruik word, dit moontlik sou wees om NW 120 direk op te skaal van loodsaanleg tot volskaal. Die reaksietoestande is gevaneer oor 'n wye bereik om die optimum prosestoestande te probeer verkry. Die roerspoed is gevarieer tussen 150 - 550 opm. Daar is gevind dat die emulsie sleur sensitief is bokant 'n roerspoed van 450 opm. Die gemete fisiese eienskappe by 'n roerspoed van 550 opm was onaanvaarbaar. Die optimum roerspoed in terme van partikelgrootte en viskositeit lê tussen 150 en 250 opm. Die reaksietemperatuur is gevarieer tussen 90 - 70°C. Die optimum temperatuur lê tussen 90 - 80 °C. Dit was moontlik om die monomeer-toevoertyd, m.a.w die reaksietyd, te verminder deur die toevoertempo van die monomere/katalis te verhoog, van 4 tot 2 ~ uur. Die metode wat deur Klein et al. (1996) ontwikkel is vir die opskalering van die roerspoed van 'n emulsiepolimerisasie reaksie is gebruik om die ekwivalente roerspoed vir die opskalering te verkry. Die opskalering van NW 120 is uitgevoer by 'n reaksietemperatuur van 85°C en 'n roerspoed van 35 opm. Die monomere/katalis is toegevoer oor 'n tydperk van 4 uur. Die verkorte reaksietyd is nie oorweeg vir die opskaleringslopie nie omdat dit nog nie seker was of die hitteverwydering van die industriële reaktor effektief genoeg sou wees om die verhoging in die reaksiewarmte-ontwikkeling, wat geassosieer word met 'n verhoging in die toevoertempo van die monomere/katalis, te kan verwyder nie. Baie goeie resultate is verkry. Die gemete fisiese eienskappe van NW 120 wat verkry is in die industriële reaktor was ongeveer dieselfde as dié wat verkry is op die loodsaanleg.