Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Immersed membrane systems hold many operational and environmental advantages in biological treatment of wastewater. However, immersed membrane filtration have only found application in niche markets to date because of higher capital and operating costs associated with membrane fouling. But with capital costs on the decline as membranes become less expensive, immersed membrane systems are increasingly considered as an attractive alternative to conventional treatment processes. Operating costs remain high however, since energy intensive techniques such as air-sparging are required to limit membrane fouling. Improving the air-scouring efficiency of air-sparged immersed membranes can significantly reduce operating costs and unlock the immersed membrane system technology to wider application. The aim of this study was to identify factors that will improve air-scouring efficiency in order to produce guidelines that will help in the development of an immersed microfiltration membrane system with a resulting lower operating cost. Although, the research was done on a flat-sheet microfiltration membrane, the guidelines obtained can be used for the development of any immersed microfiltration membrane arrangement. An airlift reactor set-up was chosen for this study. Six system hydrodynamic factors were evaluated in a factorial design to determine their effects on the cross-flow velocity profile. They were the downcomer area to riser area ratio, top clearance distance, bottom clearance distance, aeration intensity, water depth and air sparger location. It was found that the air-scouring efficiency was increased by generating a cross-flow velocity profile with increased magnitude and uniformity, but absolute uniformity of the cross-flow velocity profile was found to be a prerequisite for optimisation of air-scouring efficiency. Downcomer area to riser area ratio was found to be 99.9% significant in determining the magnitude of the cross-flow velocity profile. Two models were developed to respectively predict the relative magnitude and uniformity of the cross-flow velocity profile. By using these two models, a methodology was developed to design an airlift reactor set-up that would produce system hydrodynamics with an improved air-scouring efficiency. / AFRIKAANSE OPSOMMING: Gesonke membraanstelsels beskik oor talle bedryfs- en omgewingsvoordele in biologiese behandeling van afvalwater. Maar weens die hoër kapitaal- en bedryfskostes wat gepaardgaan met membraanbevuiling, kon gesonke membraanstelsels tot op hede nog net toepassing in nismarkte vind. Maar soos kapitaalkoste daal met al hoe goedkoper membrane beskikbaar, word gesonke membraanstelsels al hoe aanlokliker as ‘n alternatief vir konvensionele behandelingsprosesse. Bedryfskostes bly egter hoog aangesien energie-intensiewe tegnieke soos lugborreling benodig word om membraanbevuiling te vertraag. Deur die effektiwiteit van die skropaksie wat lugborreling aan gesonke membrane bied te verbeter, kan ‘n beduidende besparing in bedryfskostes teweeggebring word om sodoende die uitgebreide toepassing van gesonke membraanstelsel tegnologie moontlik te maak. Hierdie studie het ten doel gehad die identifisering van faktore wat lugskropaksie effektiwiteit kan verbeter en om riglyne op te stel vir die ontwikkeling van ‘n gesonke mikrofiltrasie membraanstelsel met gevolglik laer bedryfskostes. Alhoewel hierdie navorsing ‘n plat-blad mikrofiltrasie membraan gebruik het, kan die riglyne steeds vir enige gesonke mikrofiltrasie membraanuitleg gebruik word. Daar is besluit op ‘n lugligter-reaktor opstelling vir hierdie studie. Ses stelselhidrodinamika faktore is geëvalueer in ‘n faktoriale ontwerp om hul effekte op die kruisvloei snelheidsprofiel te bepaal. Hulle was die afvloei-area tot opvloei-area verhouding, topruimte-afstand, bodemruimte-afstand, belugtingsintensiteit, waterdiepte en belugterligging. Daar is bevind dat die lugskropaksie effektiwiteit verhoog word wanneer ‘n kruisvloei snelheidsprofiel geskep word met ‘n verhoogde grootte en gelykvormigheid, maar die absolute gelykvormigheid van die kruisvloei snelheidsprofiel is gevind om ‘n voorvereiste te wees vir optimale effektiwiteit. Afvloei-area tot opvloei-area verhouding is gevind om 99.9% beduidend te wees in die bepaling van die snelheidsprofiel se grootte. Twee modelle is ontwikkel om afsonderlik die relatiewe grootte en gelykvormigheid van die kruisvloei snelheidsprofiel te voorspel. Die modelle is in ‘n metodologie vervat vir die ontwerp van ‘n lugligter opstelling met stelselhidrodinamika wat verbeterde lugskropaksie effektiwiteit sal skep.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The world’s depleting fossil fuels and increasing greenhouse gas emissions have given rise to much research into renewable and cleaner energy. Biomass is unique in providing the only renewable source of fixed carbon. Agricultural residues such as Sugarcane Bagasse (SB) are feedstocks for ‘second generation fuels’ which means they do not compete with production of food crops. In South Africa approximately 6 million tons of raw SB is produced annually, most of which is combusted onsite for steam generation. In light of the current interest in bio-fuels and the poor utilization of SB as energy product in the sugar industry, alternative energy recovery processes should be investigated. This study looks into the thermochemical upgrading of SB by means of pyrolysis. Biomass pyrolysis is defined as the thermo-chemical decomposition of organic materials in the absence of oxygen or other reactants. Slow Pyrolysis (SP), Vacuum Pyrolysis (VP), and Fast Pyrolysis (FP) are studied in this thesis. Varying amounts of char and bio-oil are produced by the different processes, which both provide advantages to the sugar industry. Char can be combusted or gasified as an energy-dense fuel, used as bio-char fertilizer, or upgraded to activated carbon. High quality bio-oil can be combusted or gasified as a liquid energy-dense fuel, can be used as a chemical feedstock, and shows potential for upgrading to transport fuel quality. FP is the most modern of the pyrolysis technologies and is focused on oil production. In order to investigate this process a 1 kg/h FP unit was designed, constructed and commissioned. The new unit was tested and compared to two different FP processes at Forschungszentrum Karlsruhe (FZK) in Germany. As a means of investigating the devolatilization behaviour of SB a Thermogravimetric Analysis (TGA) study was conducted. To investigate the quality of products that can be obtained an experimental study was done on SP, VP, and FP. Three distinct mass loss stages were identified from TGA. The first stage, 25 to 110°C, is due to evaporation of moisture. Pyrolitic devolatilization was shown to start at 230°C. The final stage occurs at temperatures above 370°C and is associated with the cracking of heavier bonds and char formation. The optimal decomposition temperatures for hemicellulose and cellulose were identified as 290°C and 345°C, respectively. Lignin was found to decompose over the entire temperature range without a distinct peak. These results were confirmed by a previous study on TGA of bagasse. SP and VP of bagasse were studied in the same reactor to allow for accurate comparison. Both these processes were conducted at low heating rates (20°C/min) and were therefore focused on char production. Slow pyrolysis produced the highest char yield, and char calorific value. Vacuum pyrolysis produced the highest BET surface area chars (>300 m2/g) and bio-oil that contained significantly less water compared to SP bio-oil. The short vapour residence time in the VP process improved the quality of liquids. The mechanism for pore formation is improved at low pressure, thereby producing higher surface area chars. A trade-off exists between the yield of char and the quality thereof. FP at Stellenbosch University produced liquid yields up to 65 ± 3 wt% at the established optimal temperature of 500°C. The properties of the bio-oil from the newly designed unit compared well to bio-oil from the units at FZK. The char properties showed some variation for the different FP processes. At the optimal FP conditions 20 wt% extra bio-oil is produced compared to SP and VP. The FP bio-oil contained 20 wt% water and the calorific value was estimated at 18 ± 1 MJ/kg. The energy per volume of FP bio-oil was estimated to be at least 11 times more than dry SB. FP was found to be the most effective process for producing a single product with over 60% of the original biomass energy. The optimal productions of either high quality bio-oil or high surface area char were found to be application dependent. / AFRIKAANSE OPSOMMING: As gevolg van die uitputting van fossielbrandstofreserwes, en die toenemende vrystelling van kweekhuisgasse word daar tans wêreldwyd baie navorsing op hernubare en skoner energie gedoen. Biomassa is uniek as die enigste bron van hernubare vaste koolstof. Landbouafval soos Suikerriet Bagasse (SB) is grondstowwe vir ‘tweede generasie bio-brandstowwe’ wat nie die mark van voedselgewasse direk affekteer nie. In Suid Afrika word jaarliks ongeveer 6 miljoen ton SB geproduseer, waarvan die meeste by die suikermeulens verbrand word om stoom te genereer. Weens die huidige belangstelling in bio-brandstowwe en ondoeltreffende benutting van SB as energieproduk in die suikerindustrie moet alternatiewe energie-onginningsprosesse ondersoek word. Hierdie studie is op die termo-chemiese verwerking van SB deur middel van pirolise gefokus. Biomassa pirolise word gedefinieer as die termo-chemiese afbreking van organiese bio-materiaal in die afwesigheid van suurstof en ander reagense. Stadige Pirolise (SP), Vakuum Pirolise (VP), en Vinnige Pirolise word in hierdie tesis ondersoek. Die drie prosesse produseer veskillende hoeveelhede houtskool en bio-olie wat albei voordele bied vir die suikerindustrie. Houtskool kan as ‘n vaste energie-digte brandstof verbrand of vergas word, as bio-houtskoolkompos gebruik word, of kan verder tot geaktiveerde koolstof geprosesseer word. Hoë kwaliteit bio-olie kan verbrand of vergas word, kan as bron vir chemikalië gebruik word, en toon potensiaal om in die toekoms opgegradeer te kan word tot vervoerbrandstof kwaliteit. Vinnige pirolise is die mees moderne pirolise tegnologie en is op bio-olie produksie gefokus. Om die laasgenoemde proses te toets is ‘n 1 kg/h vinnige pirolise eenheid ontwerp, opgerig en in werking gestel. Die nuwe pirolise eenheid is getoets en vegelyk met twee verskillende vinnige pirolise eenhede by Forschungszentrum Karlsruhe (FZK) in Duitsland. Termo-Gravimetriese Analise (TGA) is gedoen om die ontvlugtigingskenmerke van SB te bestudeer. Eksperimentele werk is verrig om die kwaliteit van produkte van SP, VP, vinnige pirolise te vergelyk. Drie duidelike massaverlies fases van TGA is geïdentifiseer. Die eerste fase (25 – 110°C) is as gevolg van die verdamping van vog. Pirolitiese ontvlugtiging het begin by 230°C. Die finale fase (> 370°C) is met die kraking van swaar verbindings en die vorming van houtskool geassosieer. Die optimale afbrekingstemperatuur vir hemisellulose en sellulose is as 290°C en 345°C, respektiewelik, geïdentifiseer. Daar is gevind dat lignien stadig oor die twede en derde fases afgebreek word sonder ‘n duidelike optimale afbrekingstemperatuur. Die resultate is deur vorige navorsing op TGA van SB bevestig. SP en VP van bagasse is in dieselfde reaktor bestudeer, om ‘n akkurate vergelyking moontlik te maak. Beide prosesse was by lae verhittingstempo’s (20°C/min) ondersoek, wat gevolglik op houtskoolformasie gefokus is. SP het die hoogste houtskoolopbrengs, met die hoogste verbrandingsenergie, geproduseer. VP het hootskool met die hoogste BET oppervlakarea geproduseer, en die bio-olie was weens ‘n dramatiese afname in waterinhoud van beter gehalte. Die meganisme vir die vorming van ‘n poreuse struktuur word deur lae atmosferiese druk verbeter. Daar bestaan ‘n inverse verband tussen die kwantiteit en kwaliteit van die houtskool. Vinnige pirolise by die Universiteit van Stellenbosch het ‘n bio-olie opbrengs van 65 ± 3 massa% by ‘n vooraf vasgestelde optimale temperatuur van 500°C geproduseer. Die eienskappe van bio-olie wat deur die nuwe vinnige pirolise eenheid geproduseer is het goed ooreengestem met die bio-olie afkomstig van FZK se pirolise eenhede. Die houtskool eienskappe van die drie pirolise eenhede het enkele verskille getoon. By optimale toestande vir vinnige pirolise word daar 20 massa% meer bio-olie as by SP en VP geproduseer. Vinnige pirolise bio-olie het ‘n waterinhoud van 20 massa% en ‘n verbrandingswarmte van 18 ± 1 MJ/kg. Daar is gevind dat ten opsigte van droë SB die energie per enheidsvolume van bio-olie ongeveer 11 keer meer is. Vinnige pirolise is die mees doeltreffende proses vir die vervaardiging van ‘n produk wat meer as 60% van die oorspronklike biomassa energie bevat. Daar is gevind dat die optimale hoeveelhede van hoë kwaliteit bio-olie en hoë oppervlakarea houtskool doelafhanklik is.

Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: A Computational Fluid Dynamics (CFD) model was developed for the prediction of flotation rate constants in a stirred flotation tank and validated against experimental data. The model incorporated local, time-varying values of the turbulent flow field into an existing kinetic flotation model based on the Generalised Sutherland Equation to predict the overall flotation rate constant. Simulations were performed for the flotation of various minerals at different operational conditions and the predictions were compared with experimental data. It was found that the CFD-based model yielded improvements in the prediction of flotation rate constant for a range of hydrophobicities, agitation speeds and gas flow rates compared with existing methodologies, which use volume-averaged empirical expressions for flow variables. Moreover, comparing to the available CFD alternatives for the flotation modelling this approach eliminates the need for solving an extra partial differential equation resulting in a more computationally economic model. The model was developed in three stages. In the first, a single-phase model was used to establish the requirements for successful modelling of the velocity components and turbulent properties of water inside flotation tanks. Also, a novel use of the Grid Convergence Index for this application was carried out, which allowed determination of the maximum achievable reduction in numerical uncertainties through systematic grid refinement and adaptation. All subsequent simulations were performed at the optimal discretization level determined in this manner. It was found that the Moving Reference Frames (MRF) method was adequate for representation of the impeller movement when the rotational zone was located close to the impeller, using a time step advance of between 10◦ and 15◦ of impeller rotation. Comparison of the different turbulence models for the single-phase modelling revealed that the standard k-e and Large Eddy Simulation turbulence models both performed equally well and that the computational requirement was lower for the standard k-e model, making it the method of choice. Validation of the methodology was done by comparison with experimental data for two different stirred tanks including an unbaffled mixer and a fully baffled standard Rushton turbine tank. The validation against experimental data showed that the model was capable of predicting the flow pattern, turbulent properties and the generation of trailing vortices. The second stage of modelling used an Eulerian-Eulerian formulation for gasliquid modelling of gas-sparged fully baffled vessels (2.25 l, 10 l and 50 l) using a Rushton turbine. It was determined that the minimum model uncertainty resulting from simulation of the sparger was achieved using a disk sparger with a diameter equal to 40% of the impeller diameter. The only significant interfacial force was found to be the drag force, and this was included in the multiphase methodology. A parametric study on the available formulations for the drag coefficient was performed which showed that the effect of turbulence on the air bubbles can accurately be represented using the proposed model of Lane (Lane, 2006). Validation of the methodology was conducted by comparison of the available experimental gas holdup measurements with the numerical predictions for three different scales of Rushton turbine tanks. The results verified that the application of the designed sparger in conjunction with Lane drag coefficient can yield accurate predictions of the gas-liquid flow inside the flotation tank with the error percentage less than 6%, 13%, and 23% for laboratory, pilot and industrial scale Rushton turbine tanks, respectively. The last stage of this study broadened the Eulerian-Eulerian framework to predict the flotation rate constant. The spatially and temporally varying flow variables were incorporated into an established fundamental flotation model due to Pyke (Pyke, 2004) based on the Generalized Sutherland equation for the flotation rate constant. The computation of the efficiency of the flotation sub-processes also incorporated the turbulent fluctuating flow characteristics. Values of the flotation rate constants were computed and volume-weight averaged for validation against available experimental data. The numerical predictions of the flotation rate constants for quartz particles for a range of particle diameters showed improvements in the predictions when compared with values determined from existing methodologies which use spatially uniform values for the important hydrodynamic variables as obtained from empirical correlations. Further validations of the developed CFD-kinetic model were carried out for the prediction of the flotation rate constants of quartz and galena floating under different hydrophobicities, agitation speeds and gas flow rates. The good agreement between the numerical predictions and experimental data (less than 12% error) confirmed that the new model can be used for the flotation modelling, design and optimization. Considering the limited number of CFD studies for flotation modelling, the main contribution of this work is that it provides a validated and optimised numerical methodology that predicts the flotation macro response (i.e., flotation rate constant) by integrating the significance of the hydrodynamic flow features into the flotation micro-processes. This approach also provides a more economical model when it is compared to the available CFD models for the flotation process. Such an approach opens the possibility of extracting maximum advantage from the computed parameters of the flow field in developing more effective flotation devices. / AFRIKAANSE OPSOMMING: 'n Wye verskeidenheid van industriële toepassings gebruik meganies geroerde tenks vir doeleindes soos die meng van verskillende vloeistowwe, verspreiding van 'n afsonderlike fase in 'n deurlopende vloeistoffase en die skeiding van verskillende komponente in ‘n tenk. Die hoofdoel van die tesis is om ‘n numeriese model te ontwikkel vir ʼn flotteringstenk. Die kompleksiteit van die vloei (drie-dimensioneel, veelvuldige fases en volledig turbulent) maak die voorspelling van die werksverrigting van die flottasieproses moeilik. Konvensioneel word empiriese korrelasies gebruik vir modellering, ontwerp en die optimalisering van die flotteringstenks. In die huidige studie word ‘Computational Fluid Dynamics’ (CFD) egter gebruik vir die modellerings doel, aangesien dit ‘n alternatief bied vir empiriese vergelykings deurdat dit volledig inligting verskaf aangaande die gedrag van vloei in die tenk. Die model is ontwikkel in drie agtereenvolgende stadiums. Dit begin met ‘n strategie vir enkelfase modellering in die tenk, vorder dan na ‘n gas-vloeistof CFD model en brei dan die tweede stap uit om ‘n CFD model te skep vir die skeidingsproses deur flottering. ‘n Enkelfase model, gebaseer op die kontinuïteits- en momentumvergelykings, dien as basis vir die flottasie model. Die ‘Multiple Reference Frames’ (MRF) metode word gebruik om die rotasie van die stuwer na te boots, terwyl die dimensies van die rotasie-sone gekies is om die gepaardgaande onsekerhede, insluitend die model- en numeriese foute veroorsaak deur die dimensies van die roterende sones, te verminder. Die turbulensie model studie het getoon dat die standaard k-e turbulensie model redelike akkuraatheid kon lewer in die numeriese voorspellings en die resultate verskil in gemiddeld net minder as 15% van die eksperimentele lesings, terwyl die rekenaartyd min genoeg was om die simulasies op 'n persoonlike rekenaar uit te voer. Verder het die ‘Grid Convergence Index’ (GCI) metode die inherente onsekerhede in die numeriese voorspellings gerapporteer en gewys dat die onderskatting van die turbulensie wat algemeen plaasvind reggestel kan word deur van ‘Large Eddie’ (LES) of ‘Direct Numerical Simulations’ (DNS) gebruik te maak. Die metode wat ontwikkel is, is op twee tipes geroerde tenks getoets, naamlik 'n onafgeskorte menger en 'n standaard Rushton turbine tenk. Die numeriese resultate is teen eksperimentele data gevalideer en het gewys dat die model in staat is om die vloeipatrone, turbulensie einskappe en die vorming van agterblywende vortekse te voorspel. Die CFD resultate het getoon dat die vloeipatroon twee simmetriese rotasies siklusse bo en onder die roterende sone vorm, terwyl die vlak van die ooreenkoms tussen die numeriese voorspellings van die turbulente eienskappe en die eksperimentele lesings met minder as 25% verskil. As die tweede stap van hierdie navorsing is 'n Eulerian-Eulerian struktuur ontwikkel vir die gas-vloeistof modellering binne 'n standaard Rushton turbine flotteringstenk. Soos vir die enkelfase modellering is die Reynolds spanningstensor opgelos deur die standaard k-e turbulensie model, terwyl die lugborrels ingevoer/versamel is in/van die tenk deurmiddel van bron/sink terme. Verskeie ‘sparger’ rangskikkings is in die tenk geïmplementeer om die onsekerheid in die model weens die metode van luginspuiting te verminder. Verder is verskillende korrelasies vir die sleursyfer vergelyk vir laminêre en turbulente vloei in die tenk. Daar is gevind dat die skyf ‘sparger’, met 'n deursnee gelykstaande aan 40% van die stuwer deursnee, in samewerking met die voorgestelde model van Lane (Lane, 2006) vir die bepaalde sleursyfer die naaste ooreenkoms met die eksperimentele metings lewer (met 'n gemiddelde verskil van minder as 25%). 'n Vergelykende studie is ook uitgevoer om die gevolge van die gas vloeitempo en roerspoed vir drie verskillende geroerde tenks met volumes van 2.5 l, 10 l en 50 l te ondersoek. Die resultate van hierdie afdeling bevestig dat die CFD metode in staat was om die gas-vloeistof vloei in die flotteringstenk korrek te voorspel. Die veelvuldigefase model wat ontwikkel is, is uitgebrei vir flottasie modellering. Dit behels die integrasie van die CFD resultate met die fundamentele flottasie model van Pyke (Pyke, 2004) vir die flotteringstempo konstant. Die CFD model is toegerus met Pyke se model deur aanvullende gebruiker gedefinieerde funksies. Die CFD-kinetiese model is geëvalueer vir die flottering van kwartsdeeltjies en die resultate het die geloofwaardigheid van die model bevestig, aangesien die gemiddelde verskil tussen die numeriese voorspellings vir die flotteringstempo konstante en die eksperimentele data minder as 5% was. Die resultate is ook vergelyk met die analitiese berekeninge van Newell en daar is bevind dat die model vergelykbare voorspellings van die flotteringtempo konstantes lewer, met die ‘root mean square deviations’ (RMSD) gelyk of minder as die RMSD waardes vir die analitiese berekeninge. Verdere ondersoeke van die CFD-kinetiese model bestaan uit 'n parametriese studie wat die gevolge van die roertempo, gas vloeitempo en die oppervlak hidrofobisiteit op die flottering van kwarts- en galenietdeeltjies bestudeer. Die aanvaarbare ooreenkoms tussen die numeriese voorspellings en eksperimentele data (oor die algemeen minder as 12% fout) bewys dat die nuwe model gebruik kan word vir flotterings modellering en optimalisering.

Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The development of ―energycane‖ varieties of sugarcane for ethanol production is underway, targeting the use of both sugar juice (first generation ethanol) and bagasse (second generation ethanol). Nevertheless, identification of the preferred varieties represents the biggest challenge to the development of energycane due to large number of samples produced during breeding. In the present study, dilute acid pretreatment, enzymatic hydrolysis and fermentation processes were used to evaluate the processability of bagasse (fibrous residue generated after juice sugar extraction) from different varieties of sugarcane to select preferred varieties with the properties of improving combined ethanol yield (ethanol from juice and bagasse) per hectare. The impact of variety selection on combined ethanol yield (ethanol from juice and bagasse) per hectare was also assessed. In the first part of this study, 115 varieties of sugarcane originated from classical breeding and precision breeding (genetic engineering) were screened based on agronomic data and experimental data from biochemical processes (dilute acid pretreatment and enzymatic hydrolysis) applied to the bagasse fraction of each variety. The results showed wide variations in the chemical composition of bagasse between the varieties. Structural carbohydrates and lignin content ranged from 66.6 to 77.6% dry matter (DM) and 14.4 to 23.1% DM, respectively. The majority of precision breeding varieties showed higher arabinoxylan, lower lignin and lower ash content than most of classical breeding varieties. Combined sugar yield from the bagasse after pretreatment and enzymatic hydrolysis also varied significantly among the varieties. Up to 27.9 g/100g (dry bagasse) difference in combined sugar yield was observed. Combined sugar yield was inversely correlated with lignin as well as ash content, but it correlated positively with structural carbohydrates content. Total potential ethanol yields per hectare, calculated based on cane yield, soluble and non-soluble sugar content also differed significantly among the varieties (8,602−18,244 L/ha). Potential ethanol from bagasse contributed approximately one third of the total potential ethanol yield. Interestingly, some of the varieties had combined properties of high potential ethanol yield per hectare and improved bagasse convertibility. Thus, six varieties (3 from each breeding technology) were selected as preferred varieties for further investigation. To enhance sugar yield from bagasse, optimisation of pretreatment was conducted on the selected varieties. Industrial bagasse was included for comparison purposes. The pretreatment optimisation was based on maximising combined sugar yield from the combined pretreatment-hydrolysis process. A central composite design (CCD) was applied to investigate the effects of temperature, acid concentration and residence time on the responses and was later used to determine the maximum combined sugar yield. Pretreatment optimisation was conducted at gram scale (22.9 ml reactor) and at bench scale (1000 ml reactor). Significant differences in sugar yields (xylose, glucose, and combined sugar) between the varieties were observed. The combined sugar yields from the best performing varieties and industrial bagasse at optimal pretreatment-hydrolysis conditions differed by up to 34.1% and 33% at gram and bench scale, respectively. A high ratio of carbohydrates to lignin and low ash contents increased the release of sugar from the substrates. At mild pretreatment conditions, the differences in bioconversion efficiency between varieties were greater than at severe conditions. This observation suggests that under less severe conditions the conversion efficiency was largely determined by the properties of the biomass. Furthermore, it was demonstrated that the pretreatment conditions with temperature ranged from 184 to 200 °C and varying residence time to provide a severity factor between 3.51 and 3.96 was observed to be the area in common where 95% of maximum combined sugar yield could be obtained. Simultaneous Saccharification and Fermentation (SSF) was performed on the unwashed pressed-slurry from bagasse pretreatment at conditions for maximum combined sugar yield at bench scale. Batch and fed-batch SSF feeding strategy at different solid loadings and enzyme dosages were used aiming to reach an ethanol concentration of at least 40 g/L. The results revealed significant improvement in overall ethanol yield after SSF for the selected varieties (84.5–85.6%) compared to industrial bagasse (74.8%). The maximum ethanol concentration from the best performing varieties was 48.6−51.3 g/l and for poor performing varieties was 37.1−38.3 g/l. Ethanol concentration in the fermentation broth was inversely correlated with lignin content and the ratio of xylose to arabinose, but it showed positive correlation with glucose yield from pretreatment-enzymatic hydrolysis. The overall assessment of the varieties showed greater improvement in combined ethanol yields per hectare (71.1–90.7%) for the best performing varieties with respect to industrial sugarcane. The performance in terms of ethanol yields of selected varieties from a number harvest years was evaluated. The results showed considerable variations in ethanol yields across harvests. The results showed that the best variety in terms combined ethanol yield was not maintained across harvests. The differences in ethanol yields were greater among the varieties than across the harvests. Prolonged severe drought significantly affected the ethnol yields of all varieties represented by lower and intermediate lignin content for cane yield compared to that which had highest lignin content. However, carbohydrates content in the bagasse and sugar yield/recovery between the harvest years did not change for the most of the varieties. In summary, the present study provides evidence of the impact of cultivar selection and pretreatment optimisation in increasing conversion efficiency of bagasse. The results demonstrate that varieties with lower lignin and ash content, as well as highly substituted xylan resulted in higher sugar and ethanol yields. These results suggest that lower process requirements can be achieved without adversely affecting juice ethanol and cane yield per hectare. Nonetheless, an attempt to reduce lignin content in the bagasse, to reduce processing requirements for ethanol production, can also target the improvement of crop tolerance toward severe drought conditions. / AFRIKAANSE OPSOMMING: Die ontwikkeling van ―energie-riet‖ rasse vir etanol produksie is goed op dreef, waar beide die sap (eerste generasie etanol) en die bagasse (tweede generasie etanol) geteiken word. Die groot aantal monsters wat tydens teling geproduseer word, bied egter die grootste uitdaging vir die identifisering van nuwe rasse ten einde energie-riet te ontwikkel. In die huidige studie is verdunde suurvoorbehandeling, ensiematiese hidrolise en fermentasie-prosesse gebruik om die verwerkbaarheid van bagasse (veselagtige residu gegenereer na sap suiker ekstraksie) van verskillende suikerrietrasse te evalueer om nuwe variëteite te selekteer wat eienskappe van verbeterde gekombineerde etanolopbrengs (etanol van sap en bagasse) per hektaar toon. Die impak van variëteit-seleksie op gekombineerde etanol opbrengs (etanol van sap en bagasse) per hektaar is ook beoordeel. In die eerste deel van hierdie studie het uit ‗n siftingsproses van 115 suikerriet rasse bestaan wat deur klassieke en presisie (geneties gemodifiseerde) teling gegenereer is. Die sifting was op agronomiese data gebaseer, asook op data van verdunde suur voorafbehandeling en ensimatiese hidrolise eksperimente wat op die bagasse fraksie van elke ras uitgevoer is. Die resultate het op groot variasie in die chemiese samestelling van die bagasse van verskillende rasse gedui. Die strukturele koolhidrate het tussen 66.6 en 77.6% droë massa (DM) gewissel, terwyl die lignien inhoud ‗n variasie van 14.4 en 23.1% DM getoon het. Verder het meeste van die presisie-teling variëteite ‗n hoër arabinoxilaan, maar ‗n laer lignien en as-inhoud as meeste van die klassieke teling rasse gehad. Die gekombineerde suikeropbrengs (GSO) van die bagasse na voorafbehandeling en ensimatiese hidrolise het ook beduidend tussen rasse gewissel, waar ‗n verskil van tot 27.9 g/100g (droë bagasse) waargeneem is. Daar was ‗n omgekeerde korrelasie tussen die gekombineerde suikeropbrengs en die lignien en as-inhoud gewees, maar die opbrengs het ‗n sterk positiewe korrelasie met die strukturele koolhidrate getoon. Die totale potensiële etanol opbrengs per hektaar wat vanaf die suikerriet se oplosbare en nie-oplosbare suikerinhoud bereken is, het ook beduidend tussen rasse verskil (8,602−18,244 L/ha), waar die potensiële etanol opbrengs van die bagasse gedeelte ongeveer een derde van die totale potensiële etanol opbrengs beslaan het. Interessante bevindinge het op sommige rasse met gekombineerde eienskappe van hoë potensiële opbrengs per hektaar asook ‗n hoë omskakelingsvermoë gedui. Derhalwe is ses variëteite (drie van elke telingstegnologie) as voorkeurvariëteite vir verdere studie gekies. Om die etanol opbrengs vanaf die bagasse te verbeter was voorafbehandeling van die voorkeurvariëteite geoptimeer, en waar industriële bagasse vir vergelykingsdoeleindes ingesluit was. Vir die optimering was dit ten doel gestel om die gekombineerde suikeropbrengs van die gekombineerde voorafbehandeling-hidrolise proses te maksimeer. ‗n Sentrale saamgestelde ontwerp (SSO) is gebruik om die effek van temperatuur, suurkonsentrasie en residensietyd op die responsveranderlikes vas te stel wat uiteindelik gebruik is om die maksimum gekombineerde suikeropbrengs te bepaal. Die optimering van die voorafbehandeling is op gram-skaal in ‗n 22.9 ml reaktor, asook op bank-skaal in ‗n 1000 ml reaktor uitgevoer. Beduidende verskille in die suikeropbrengs (xilose, glukose en gekombineerde suiker) is tussen die voorkeurrasse waargeneem. Tussen die rasse wat die beste gevaar het, asook die industriële bagasse, het die gekombineerde suikeropbrengs by optimale voorafbehandeling-hidrolise toestande onderskeidelik met tot 34.1% en 33% op gram-skaal en bank-skaal gevarieer. ‗n Hoë verhouding van koolhidrate tot lignien, asook ‗n lae as-inhoud het tot ‗n toename in die vrystelling van suiker uit die substraat gelei. By matige voorafbehandelingstoestande was die verskille in omskakelingseffektiwiteit tussen rasse groter as onder hewige toestande, wat daarop gedui het dat omskakelingseffektiwiteit grotendeels deur die eienskappe van die biomassa bepaal is. Verder is daar ook gedemonstreer dat die voorbehandelingsomstandighede met temperatuur tussen 184 en 200ºC en verandering van die residensietyd om 'n hewigheidsfaktor van tussen 3.51 en 3.96 te verskaf, 'n gemeenskaplike area gelewer het waar 95% van maksimum gekombineer suiker opbrengs (GSO) verkry kon word. Gelyktydige versuikering en fermentasie (GVF) is na voorafbehandeling op ongewaste, gepersde bagasse substraat by toestande vir die maksimum gekombineerde suikeropbrengs op bank-skaal uitgevoer. Bondel en voerbondel SSF voerstrategie by verskillende vaste ladings en ensiemdoserings is gebruik om 'n etanol konsentrasie van ten minste 40 g/L te bereik. Ná GVF was die algehele etanol opbrengs vir die voorkeurvariëteite (84.5–85.6%) beduidend beter relatief tot die industriële bagasse (74.8%). Die maksimum etanol opbrengs na SSF van die rasse met die beste prestasie was 48.6-51.3 g/L en 37.1-38.3 g/L vir rasse wat swak presteer het. Die etanol konsentrasie in die fermentasiesop was omgekeerd met lignien en die verhouding van xilose tot arabinose gekorreleer, maar was duidelik positief met die glukose opbrengs vanaf voorafbehandeling-hidrolise gekorreleer. ‗n Algemene assessering het op ‗n duidelike verbetering van die voorkeurvariëteite in terme van gekombineerde etanol opbrengs per hektaar gedui (71.1–90.7%), relatief tot die industriële suikerriet. Die prestasie in terme van etanol opbrengs van geselekteerde variëteite is oor 'n reeks oesjare ge-evalueer. Die resultate het aansienlike variasies in etanol opbrengs oor oesjare getoon. Die resultate het gewys dat die beste variëteite in terme van gekombineerde etanol opbrengs nie volhou is oor oeste nie. Die verskille in etanol opbrengste tussen variëteite was groter as die verskille oor oesjare. Verlengde ernstige droogte het die etanol opbrengs van alle variëteite met laer en intermediere lignien inhoud vir rietopbrengs aansienlik beinvloed, in vergelyking met dié wat die hoogste lignien inhoud gehad het. Die koolhidraatinhoud in die bagasse en suiker opbrengs/lewering tussen die oesjare het vir die meeste variëteite egter nie gewissel nie. Ter opsomming, die huidige studie verskaf bewyse van die impak van kultivarseleksie en voorbehandelings optimisering op die verhoging van die omskakelings-doeltreffendheid van bagasse. Die resultate wys dat variëteite met laer lignien- en asinhoud, en hoogs-gesubstitueerde xilaan hoër suiker- en etanol opbrengs gelewer het. Hierdie resultate stel voor dat verminderde voorbehandelingsvereistes bereik kan word sonder om die sap etanol en rietopbrengs per hektar te benadeel. Nieteenstaande, 'n poging om die lignien inhoud van die bagasse te verminder om die verwerkingsvereistes vir etanolproduksie te verminder, kan ook die verbetering van gewas-toleransie tov ernstige droogte-toestande teiken.

Thesis (MScEng)--University of Stellenbosch, 2006. / ENGLISH ABSTRACT: Behaviour of palladium, platinum, copper, chloride anions, hydrogen cations, the l3-hydroxyoxime LIX 84-1 and the primary amine Primene JM-T during the extraction of Pd at the Anglo Platinum Precious Metals Refinery (PMR). The extractions of Pd, Pt and Cu into the organic phase were modelled as first-order reactions, with respect to the concentration of Pd, Pt and Cu in the aqueous phase, respectively. The movement of all other species are based on the stoichiometry of the three extraction reactions. Parameters found from literature and from previous experimental work by Johnson Matthey Technology Centre and Anglo Research (previously the Anglo Platinum Research Centre) generally describe the thermodynamic and kinetic behaviour of Pd extraction. Parameters for Pt and Cu co-extraction have been hypothesised and need to be confirmed through adequate experimental testwork. The model is fully functional and, upon completion of the simulation, all species' concentration profiles are produced. Eight mixers have been modelled as two continuous stirred tank reactors (CSTRs) with counter-current flow, and the concentration profiles are given as functions of the residence time of the two CSTRs. A secondary model has been created to facilitate future validation of the model by mimicking the movement of species in titanium unit cell batch extraction experiments. Both the primary and secondary models are based on identical thermodynamic and kinetic parameters for all reactions involved. Due to the fact that possibly inaccurate parameters were used in the construction of the Pd extraction model, the outputs shown serve to illustrate the value of the simulation model once all unknown parameters have been quantified through adequate experimental work. Keywords: Anglo Platinum, PMR, solvent extraction, kinetics, simulation. / AFRIKAANSE OPSOMMING: Model is met behulp van Matlab en Simulink ontwikkel om die beweging van palladium, platinum, koper, chloried- en waterstofione, die hidroksie-oksiem LIX 84-1 en die primere amien Primene JM-T tydens die ekstraksie van Pd by die Anglo Piatinum Precious Metals Refinery (PMR) te simuleer. Die ekstraksie van Pd, Pt and Cu na die organiese fase is gemodelleer as eerste-orde reaksies, met betrekking tot die konsentrasie van Pd, Pt en Cu in die water-fase, respektiewelik. Die beweging van alle ander chemiese spesies is gebaseer op die stoichiometrie van die drie ekstraksiereaksies. Parameters gevind uit literatuur en vanaf vorige eksperimentele werk, gedoen deur Johnson Matthey Tegnologiesentrum en Anglo Research (voorheen die Anglo Platinum Navorsingsentrum), beskryf die termodinamiese en kinetiese gedrag van elemente betrokke in Pd ekstraksie. Parameters vir pt en Cu ko-ekstraksie is aangeneem en hierdie waardes moet deur die nodige eksperimentele toetswerk bepaal word, alvorens dit in die model ingesluit word. Die model is ten volle funksioneel en, met die voltooiing van simulasies, word alle spesies se konsentrasies in die organiese en water-fase vertoon. Agt mengers is gemodelleer as twee kontinue gemengde-tenk reaktore waardeur die twee fases in teenoorgestelde rigtings vloei, en die konsentrasieprofiele van al die spesies word as funksies van die mengsel-verblyftyd in die twee reaktore gegee. 'n Sekondere model is ontwikkel om toekomstige validasie van die primere model te bewerkstellig. Waar die primere gebaseer is op die vloei-uitleg van die Pd ekstraksie-baan by PMR, is die sekondere model gebaseer op die toepaslike kondisies in toetswerk wat algemeen gedoen word in 'n titanium eenheids-ekstraksiesel. Beide die primere en sekondere modelle gebruik identiese termodinamiese en kinetiese parameters vir alle betrokke ekstraksiereaksies. Omdat moontlike onakkurate parameters in die simulasiemodel gebruik word, wys die uitsette van die model slegs die funksionaliteit wat die simulasie-model sal he sodra alle parameters deur die nodige eksperimentele toetswerk bepaal is. Sleutelwoorde: Anglo Platinum, PMR, ekstraksie, kinetika, simulasie.

Thesis (PhD (Process Engineering)--Stellenbosch University, 2006. / My applied engineering research and industrial application work of the past 20 years is presented in this dissertation. It is the conjecture of my work that only if thorough first principles knowledge of the depth of process metallurgy and recycling is available, can meaningful first principles environmental models be developed. These models can then evaluate technology, provide well argued and first principles environmental information to our tax paying consumer society as well as to legislators and environmentalists. Only through this path can one estimate the limits of recycling and its technology, hence evaluate the true boundaries of sustainability. My work with students has presently culminated in the detailed modelling and simulation of recycling systems for post-consumer goods. Notably the models are finding an application in the prediction of legally required recycling rates for automobiles. The models provide first principles arguments for less stringent EU recycling legislation and the integration of the first principles models in computer aided design tools of the automotive industry as part of a large EU 6th Framework (project managed by Volkswagen and the other European car producers). Presently these models are also being converted to model the Waste Electric and Electronic Equipment (WEEE) as well as water recycling systems respectively, both for industry in The Netherlands. This unique rigorous integration of systems engineering, reactor technology and process control theory is the basis of all my work to describe recycling systems as dynamic feedback control loops. My large body of acquired industrial knowledge renders these models practical and can hence be used by the automotive and recycling industries. The origins of this work may be found in the various cited publications and reports to industry by myself (due to my close association with industry as well as industrial experience) over the past 20 years as well as the work of my students, covering topics such as: • system optimization models for flotation, mineral beneficiation and recycling systems and applying these for design for recycling and argue for better/improved first-principles based legislation, • industrial measurement, modelling and simulation of industrial extractive process pyrometallurgical reactors as well waste incinerators and recycling plants, • various activities in other areas such as hydrometallurgy, clean and new breakthrough technology, and • process control of industrial metallurgical reactors by among others the application of artificial intelligence techniques. All the ideas of the last years have been worked out with students and have been summarized in our book: “The Metrics of Material and Metal Ecology, Harmonizing the resource, technology and environmental cycles”.

Thesis (PhD)--University of Stellenbosch, 2004. / 271 Leaves printed single pages, preliminary pages i-xviii and 253 numberd pages. Includes bibliography. List of figures, List of tables. / ENGLISH ABSTRACT: A Neurocontrol Paradigm for Intelligent Process Control using Evolutionary Reinforcement Learning Balancing multiple business and operational objectives within a comprehensive control strategy is a complex configuration task. Non-linearities and complex multiple process interactions combine as formidable cause-effect interrelationships. A clear understanding of these relationships is often instrumental to meeting the process control objectives. However, such control system configurations are generally conceived in a qualitative manner and with pronounced reliance on past effective configurations (Foss, 1973). Thirty years after Foss' critique, control system configuration remains a largely heuristic affair. Biological methods of processing information are fundamentally different from the methods used in conventional control techniques. Biological neural mechanisms (i.e., intelligent systems) are based on partial models, largely devoid of the system's underlying natural laws. Neural control strategies are carried out without a pure mathematical formulation of the task or the environment. Rather, biological systems rely on knowledge of cause-effect interactions, creating robust control strategies from ill-defined dynamic systems. Dynamic modelling may be either phenomenological or empirical. Phenomenological models are derived from first principles and typically consist of algebraic and differential equations. First principles modelling is both time consuming and expensive. Vast data warehouses of historical plant data make empirical modelling attractive. Singular spectrum analysis (SSA) is a rapid model development technique for identifying dominant state variables from historical plant time series data. Since time series data invariably covers a limited region of the state space, SSA models are almost necessarily partial models. Interpreting and learning causal relationships from dynamic models requires sufficient feedback of the environment's state. Systemisation of the learning task is imperative. Reinforcement learning is a computational approach to understanding and automating goal-directed learning. This thesis aimed to establish a neurocontrol paradigm for non-linear, high dimensional processes within an evolutionary reinforcement learning (ERL) framework. Symbiotic memetic neuro-evolution (SMNE) is an ERL algorithm developed for global tuning of neurocontroller weights. SMNE is comprised of a symbiotic evolutionary algorithm and local particle swarm optimisation. Implicit fitness sharing ensures a global search and the synergy between global and local search speeds convergence.Several simulation studies have been undertaken, viz. a highly non-linear bioreactor, a rigorous ball mill grinding circuit and the Tennessee Eastman control challenge. Pseudo-empirical modelling of an industrial fed-batch fermentation shows the application of SSA for developing partial models. Using SSA, state estimation is forthcoming without resorting to fundamental models. A dynamic model of a multieffect batch distillation (MEBAD) pilot plant was fashioned using SSA. Thereafter, SMNE developed a neurocontroller for on-line implementation using the SSA model of the MEBAD pilot plant. Both simulated and experimental studies confirmed the robust performance of ERL neurocontrollers. Coordinated flow sheet design, steady state optimisation and nonlinear controller development encompass a comprehensive methodology. Effective selection of controlled variables and pairing of process and manipulated variables were implicit to the SMNE methodology. High economic performance was attained in highly non-linear regions of the state space. SMNE imparted significant generalisation in the face of process uncertainty. Nevertheless, changing process conditions may necessitate neurocontroller adaptation. Adaptive neural swarming (ANS) allows for adaptation to drifting process conditions and tracking of the economic optimum online. Additionally, SMNE allows for control strategy design beyond single unit operations. SMNE is equally applicable to processes with high dimensionality, developing plant-wide control strategies. Many of the difficulties in conventional plant-wide control may be circumvented in the biologically motivated approach of the SMNE algorithm. Future work will focus on refinements to both SMNE and SSA. SMNE and SSA thus offer a non-heuristic, quantitative approach that requires minimal engineering judgement or knowledge, making the methodology free of subjective design input. Evolutionary reinforcement learning offers significant advantages for developing high performance control strategies for the chemical, mineral and metallurgical industries. Symbiotic memetic neuro-evolution (SMNE), adaptive neural swarming (ANS) and singular spectrum analysis (SSA) present a response to Foss' critique. / AFRIKAANSE OPSOMMING: 'n Neurobeheer paradigma vir intelligente prosesbeheer deur die gebruik van evolusionêre versterkingsleer Dit is 'n komplekse ontwikkelingstaak om menigte besigheids- en operasionele doelwitte in 'n omvattende beheerstrategie te vereenselwig. Nie-lineêriteite en vele komplekse prosesinteraksies kombineer om ingewikkelde aksie-reaksie verwantskappe te vorm. Dit is dikwels noodsaaklik om hierdie interaksies omvattend te verstaan, voordat prosesbeheer doelwitte doeltreffend gedoen kan word. Tog word sulke beheerstelsels dikwels saamgestel op grond van kwalitatiewe kriteria en word ook dikwels staatgemaak op historiese benaderings wat voorheen effektief was (Foss, 1973). Dertig jaar na Foss se kritiek, bly prosesbeheerstelsel ontwerp 'n heuristiese saak. Die biologiese prosessering van informasie is fundamenteel verskillend van metodes wat gebruik word in konvensionele beheertegnieke. Biologiese neurale meganismes (d.w.s., intelligente stelsels) word gebaseer op gedeeltelike modelle, wat grotendeels verwyderd is van die onderskrywende natuurwette. Neurobeheerstrategieë word toegepas sonder suiwer wiskundige formulering van die taak of die omgewing. Biologiese stelsels maak eerder staat op kennis van aksie-reaksie verhoudings en skep robuuste beheerstrategieë van swak gedefineerde dinamiese stelsels. Dinamiese modelle is of fundamenteel of empiries. Fundamentele modelle word ontwikkel vanaf eerste beginsels en word tipies uit algebraïese en differensiële vergelykings saamgestel. Modellering vanaf eerste beginsels is beide tydrowend en duur. Groot databasisse van historiese aanlegdata maak empiriese modellering aantreklik. Singuliere spektrumanalise (SSA) maak die vinnige ontwerp van empiriese modelle moontlik, waardeur dominante veranderlikes vanaf historiese tydreekse onttrek kan word. Aangesien tydreeksdata slegs 'n gedeelte van die prosesomgewing verteenwoordig, is SSA modelle noodwendig gedeeltelike modelle. Die interpretasie en aanleer van kousale verhoudings vanaf dinamiese modelle vereis voldoende terugvoer van omgewingstoestande. Die leertaak moet sistematies uitgevoer word. Versterkingsleer is 'n ramingsbenadering tot 'n doelwit-gedrewe leerproses. Hierdie tesis bewerkstellig 'n neurobeheerparadigme vir nie-lineêre prosesse met hoë dimensies binne 'n evolusionêre versterkingsleer (EVL) raamwerk. Simbiotiese, memetiese neuro-evolusie (SMNE) is 'n EVL algoritme wat ontwikkel is vir globale verstelling van die gewigte van ‘n neurobeheerder. SMNE is saamgestel uit 'n simbiotiese evolusionêre algoritme en 'n lokale partikelswerm-algoritme. Implisiete fiksheidsdeling verseker 'n globale soektog en die sinergie tussen globale en lokale soektogte bespoedig konvergensie.Verskeie simulasie studies is onderneem, o.a. die van 'n hoogs nie-lineêre bioreaktor, 'n balmeulaanleg en die Tennessee Eastman beheer probleem. Empiriese modellering van 'n industriële enkelladingsfermentasie demonstreer die aanwending van SSA vir die ontwikkeling van gedeeltelike modelle. SSA benader die toestand van 'n dinamiese stelsel sonder die aanwending van fundamentele modellering. 'n Dinamiese model van 'n multi-effek-enkelladingsdistillasie (MEBAD) proefaanleg is bewerkstellig deur die gebruik van SSA. Daarna is SMNE gebruik om 'n neurobeheerder te skep vanaf die SSA model vir die beheer van die MEBAD proefaanleg. Beide simulasie en eksperimentele studies het die robuuste aanwending van EVL neurobeheerders bevestig. Die gekoördineerde ontwerp van vloeidiagramme, gestadigde toestand-optimering en nie-lineêre beheerderontwikkeling vereis 'n omvattende metodologie. Beheerveranderlikes en die koppeling van proses- en uitvoerveranderlikes is implisiet en effektief. Maksimale ekonomiese aanwins was moontlik in hoogs nie-lineêre dele van die toestandsruimte. SMNE het besondere veralgemening toegevoeg tot neurobeheerderstrategieë ten spyte van prosesonsekerhede. Nietemin, veranderende prosestoestande mag neurobeheerderaanpassing genoodsaak. Aanpasbare neurale swerm (ANS) algoritmes pas neurobeheerders aan tydens veranderende proseskondisies en volg die ekonomiese optimum, terwyl die beheerder die proses beheer. SMNE bewerkstellig ook die ontwikkeling van beheerstrategieë vir prosesse met meer as een eenheidsoperasie. SMNE skaal na prosesse met hoë dimensionaliteit vir die ontwikkeling van aanlegwye beheerstrategieë. Talle kwelvrae in konvensionele aanleg-wye prosesbeheer word deur die biologies gemotiveerde benadering van die SMNE algoritme uit die weg geruim. Toekomstige werk sal fokus op die verfyning van beide SMNE en SSA. SMNE en SSA bied 'n nie-heuristiese, kwantitatiewe benadering wat minimale ingenieurskennis of oordeel vereis. Die metodologie is dus vry van subjektiewe ontwerpsoordeel. Evolusionêre versterkingsleer bied talle voordele vir 'n ontwikkeling van effektiewe beheerstrategieë vir die chemiese, mineraal en metallurgiese industrieë. Simbiotiese memetiese neuro-evolusie (SMNE), aanpasbare neurale swerm metodes (ANS) en singulêre spektrum analise (SSA) gee antwoord op Foss se kritiek.

Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: In the developed and developing world, the use of lipids for the production of alkyl esters, also known as biodiesel, showed phenomenal growth during the ten year period up to the end of 2007. The main sources for these lipids are the oils extracted from oil seeds such as soya-, palm-, and rape seed, but other products in the food chain such as waste cooking oil (yellow grease) and animal fats are also used. In Africa and Asia vast tracks of land not previously tilled, are now being cultivated to yield oils which are not edible and in a number of countries intensive research is focused on lipid producing species such as algae. Meanwhile more evidence is coming to the fore pronouncing biodiesel and other first generation biofuels not to be the panacea for the predicament the world is facing on unbridled population growth, energy security concerns and environmental issues such as indirect land use changes, global warming and climate changes. The acceptance of the National Biofuels Industrial Strategy at Cabinet level has not yet resulted in significant commensurate activity in South Africa. The availability, other uses and volumes of selected feed stocks for biodiesel production invite debate on the choice between food- and energy security and the appropriateness of some identified socio-economical and socio-political drivers for a viable industry. Somehow the unique characteristics of South Africa and its resources seem not to feature in debate and constraints on the production of biodiesel, as described in this dissertation. The conventional process routes for commercial biodiesel production are based on a mature technology which has inherent pollution and economical limitations. This called for a detailed critical evaluation on process routes more environmentally friendly or involving fewer unit processes generating more desirable products, albeit with more severe process conditions. By comparison, the homogeneous alkali catalyst alcoholysis (HACA), the enzymatic catalyst alcoholysis (ECA) and the super critical alcoholysis (SCA) process routes as developed in this study, are found to be competitive on total manucturing costs as assessed, if results emanating from selected sensitivity analyses and optimisation studies, are accepted. The total manufacturing and operating costs in the selected process routes as estimated, assuming the same capacities for commercial biodiesel production, are dominated by feed stock costs. Incentives on depreciation and fuel levies are deemed not effective, if costs are compared to the price of fossil diesel at the retail level – October 2011. It is concluded that using the feed stocks indicated in the Strategy, commercial biodiesel production is not economically feasible in South Africa at present. In this study process routes and feed stocks were identified that can change this position. Note should be taken of the intensive research activities being conducted on second generation technologies and biorefineries in the developed world, as discussed in this dissertation. / AFRIKAANSE OPSOMMING: In die ontwikkelde en ontwikkelende wêreld het die gebruik van vette vir die produksie van alkielesters, ook bekend as biodiesel, in die tienjaarperiode tot die einde van 2007 fenomenale groei getoon. Die hoofbronne vir hierdie lipiede is die olies onttrek van oliesade soos soja-, palm-, en raapsaad, maar ander produkte in die voedselketting soos gebruikte kookolie en dierevette word ook gebruik. In Afrika en Asië word uitgestrekte stukke grond voorheen onbewerk, nou bewerk om olies wat nie eetbaar is nie, op te lewer, en in verskeie lande word intensiewe navorsing op vetproduserende spesies soos alge gedoen. Intussen kom meer bewyse na vore wat verklaar dat biodiesel en ander eerste-generasie biobrandstowwe nie die wondermiddel is vir die moeilike posisie wat die wêreld in die gesig staar oor onbeteuelde bevolkingsaanwas, kwellings oor energiesekuriteit en omgewingskwessies soos indirekte grondverbruike, aardverwarming en klimaatsveranderings nie . Die aanvaarding van die Nasionale Biobrandstowwe Industriële Strategie op kabinetsvlak het nog nie verhoogde soortgelyke aktiwiteite in Suid-Afrika tot gevolg gehad nie. Die beskikbaarheid, gebruike en volumes van gekose grondstowwe, lok debatte uit oor die keuse tussen voedsel- en energiesekuriteit en die toepaslikheid van sekere geïndentifiseerde sosio-ekonomiese en sosio-politieke stimulante vir ‘n lewensvatbare nywerheid. Op een of ander manier is die unieke kenmerke van Suid- Afrika en sy bronne nog nie in die debat op die knelpunte van biodiesel nie, soos beskryf in hierdie proefskrif. Die gewone prosesroetes vir kommersiële produksie van biodiesel is gebaseer op ‘n beproefde tegnologie met inherente besoedelings- en ekonomiese beperkings. Dit het gevra vir ‘n uitvoerige kritiese evaluasie van meer omgewingsvriendelike- en minder eenheidsprosesse wat meer gewensde produkte genereer, al is dit met erger prosesbepalings. By vergelyking, is dit bevind dat die homogene alkali-katalisator- alkoholisis (HAKA), ensiem-katalisator-alkoholisis (EKA) en die superkritiese-alkoholisis (SKA) prosesroetes soos in hierdie studie ontwikkel, mededingend is op ‘n totale vervaardigingskoste-vlak, as die resultate wat spruit uit geselekteerde sensiwiteitsanalises en optimiseringsstudies, aanvaar word. Die totale vervaardigings- en bedryfskostes soos beraam vir die gekose prosesroetes vir kommersiële biodieselvervaardiging vir dieselfde deursette, word oorheers deur grondstofkostes. Aansporings op afskrywings en brandstofheffings word gesien as nie effektief nie, as kostes vergelyk word met die prys van fossieldiesel op kleinhandelsvlak – Oktober 2011. Die gevolgtrekking word gemaak dat met die grondstowwe aangedui in die Strategie, kommersiële biodieselvervaardiging tans nie ekonomies gangbaar is vir Suid-Afrika nie. In hierdie studie is prosesroetes en grondstowwe geïdentifiseer wat die posisie kan verander. Kennis moet geneem word van die intensiewe navorsingsaktiwiteite op tweede-geslag tegnologieë en bioraffinaderye in die ontwikkelde wereld, soos in hierdie proefskrif bespreek.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The extraction of hemicelluloses prior to pulping that would have been dissolved in black liquor during pulping process, is an attractive alternative for pulp and paper mills as they, in addition to their core products, can increase their revenue by producing biofuels, biopolymers, paper additives and other chemicals. However, the amount of hemicelluloses extracted will be limited by the requirement to maintain pulp yield and pulp quality in comparison to existing pulping processes. In the present study, mild alkaline (NaOH) and dilute sulphuric acid conditions were used to extract hemicelluloses from Eucalyptus grandis, giant bamboo (Bambusa balcooa) and sugarcane (Saccharum officinarum) bagasse (SCB) prior to kraft or sodaAQ pulping processes. The effects of catalyst concentration, temperature and reaction time on hemicelluloses pre-extraction were studied, using a statistical experimental design to investigate conditions under which hemicelluloses could be extracted prior to alkaline pulping with minimal interference on cellulose (glucan) content. Subsequently, selected pre-extracted materials were subjected to kraft or sodaAQ pulping to evaluate the effect of the hemicelluloses pre-extraction on cooking chemicals, pulp yield and properties. This study also included evaluation of hot water hemicelluloses pre-extraction of SCB as it was part of a dilute sulphuric acid experimental design. The pulp yield, cooking chemicals and handsheet strength properties were compared with those obtained from kraft or sodaAQ pulping of non extracted raw materials. The results showed that alkaline pre-extraction options investigated preserves the pulp yield with minimal effect on handsheet strength properties depending on the choice of the subsequent pulping method while a fraction of xylan was extracted in polymeric form. In addition, less active alkali was required to delignify the xylan extracted materials. The integration of hemicelluloses pre-extraction by alkaline methods into a kraft pulping process was preferred for giant bamboo and E. grandis since it maintained pulp yields at desired industrial levels of 50%, and pulps within a bleachable kappa number range. Another advantage observed was the reduction in total cooking active alkali required to delignify alkaline extracted giant bamboo or E. grandis by 8or 3 percentage points respectively. However, the compromise to maintain the pulp yield was obtained when only 13.6% or 12.4% polymeric xylan was solubilised from giant bamboo or E. grandis respectively. Slight improvement in burst index of the handsheet was observed for extracted giant bamboo. On the other hand, pulp viscosity was increased by 13% due to the removal of low molecular weight hemicelluloses, while the breaking strength of the handsheet was also increased by 8.9% for pulps produced from extracted E. grandis. In the case of sugarcane bagasse, hemicelluloses pre-extraction by alkaline methods integrated well with the sodaAQ pulping process. It enabled a xylan recovery of 69.1%, while providing pulp with higher screened pulp yield (45.0%), with an advantageous decrease in kappa number (15.5). The handsheet tear index was superior without reduction in viscosity compared to pulp produced from non extracted SCB. On the contrary, results obtained from optimised dilute sulphuric acid pre-extraction of all the tested feedstocks were found to negatively impact subsequent kraft or sodaAQ pulping processes resulting in lower pulp yields and poorer strengths properties. Nonetheless, the differences were better when sodaAQ pulping was used compared to kraft pulping. SodaAQ protects the carbohydrates against the peeling reaction under alkaline medium. Conversely, pre-extraction of SCB with hot water resulted in low concentration of xylooligomers (5.7%), while the subsequent sodaAQ pulping resulted in no pulp yield reduction. The tear index and optical brightness of the handsheet papers produced from hot water extracted SCB were slightly improved while the breaking length, tensile and burst indexes were similar to those of pulps produced from non extracted SCB fibres. Of equal importance were the observed higher tear and burst indexes of handsheets produced from giant bamboo compared to E. grandis for both extracted and non extracted materials prepared under similar pulping processes. The advantage of bamboo was due to the larger fibre length and different morphological properties to those of hardwoods. However, the pulps produced from giant bamboo showed higher kappa numbers than those pulps produced from E. grandis due to the high condensation behaviour of bamboo lignins under alkaline conditions. Higher kappa numbers explained the higher demand for subsequent bleaching chemicals. In conclusion, the pulp mill biorefinery concept through hemicelluloses pre-extraction with NaOH can be achieved with modified kraft pulping or the sodaAQ pulping processes, but it depends on the type of raw material, extraction method and quality and performance requirements of a particular paper. The low pulping chemicals demand, comparable pulp yields and the improvement in some physico-chemical properties of the pulps from preextracted materials were observed. Furthermore, owing to xylan pre-extraction a larger amount of (extracted) material could be loaded into the digester as when non-extracted materials were used. / AFRIKAANSE OPSOMMING: Ekstraksie van hemiselluloses wat tydens verpulping in die swartloog opgelos word, bied ‘n aantreklike alternatief aan pulp- en papiermeulens om, addisioneel tot hul hoofprodukte, hul inkomste deur die vervaardiging van biobrandstowwe, biopolimere, papierbymiddels en ander chemikalië, daardeur te kan verhoog. Die hoeveelheid hemiselluloses wat ge-ekstraheer kan word, sal egter beperk word deur die vereiste dat pulpopbrengs en –kwaliteit tydens bestaande verpulpingsprosesse gehandhaaf moet word. In hierdie ondersoek is matige alkaliese (NaOH) en verdunde swawelsuurtoestande gebruik om hemiselluloses vóór kraft- of natriumantrakinoonverpulping uit Eucalyptus grandis, reuse bamboes (Bambusa balcooa) en suikerriet (Saccharum officinarum) bagasse, mee te ekstraheer. Die invloed van katalisatorkonsentrasie, temperatuur en reaksietyd is mbv ‘n statistiese, eksperimentele ontwerp ondersoek om die toestande te bepaal waaronder hemiselluloses, met minimale effek op die sellulose (glukaan) –inhoud, vóór alkaliese verpulping ge-ekstraheer kan word. Die pre-ge-ekstraheerde materiale, met hoë glukaan- en voldoende hemisellulosesinhoud, is vervolgens aan kraft- en natriumantrakinoonverpulping onderwerp om die invloed van pre-ekstraksie van hemiselluloses op die verpulpingsreagense, pulpopbrengs en - eienskappe vas te stel. Hierdie studie het ook die evualering van warmwater hemisellulosespre-ekstraksie van suikerrietbagasse, wat deel is van ‘n verdunde swawelsuur eksperimentele uitleg, ingesluit. Pulpopbrengs, die hoeveelheid verpulpingsreagense en handveleienskappe van dieselfde materiale wat nie vooraf ge-ekstraheer is nie, is vergelyk. Die resultate toon dat alkaliese pre-ekstraksie metodes wat ondersoek is die pulpopbrengs met minimale effek op handvel sterkte-eienskappe afhangende van die keuse van daaropvolgende pulpmetode kon handhaaf terwyl ‘n fraksie van xilaan in polimeriese vorm ge-ekstraheer is. Addisioneel, is minder aktiewe alkali benodig om die xilaan ge-ekstraheerde materiale te delignifiseer. Die integrasie van hemisellulosespre-ekstraksie dmv alkaliese metodes tydens ‘n kraft verpulpingsproses is vir reuse bamboes en E. grandis verkies omdat pulpopbrengste op ideale industriële vlakke van 50% gehandhaaf en is en pulp in ‘n bleikbare kappa nommergebied interval kon lewer. ‘n Verdere voordeel wat waargeneem is was die vermindering in die totale gekookte aktiewe alkali benodig vir reuse bamboes of E. grandis met 8 of 3 persentasiepunte onderskeidelik. Die kompromie om die pulpopbrengs te handhaaf is verkry toe slegs 13.6% of 12.4% polimeriese xilaan opgelos is vanuit reuse bamboes of E. grandis onderskeidelik. ‘n Effense verbetering in bars-indeks van die handvelle is waargeneem vir ge-ekstraheerde reuse bamboes. Pulpviskositeit het met 13% gestyg agv die verwydering van die lae molekulêre massa hemiselluloses, terwyl breeksterkte van handvelle ook met 8.9% toegeneem het vir pulp verkry uit pre-gekstraheerde E. grandis. NaOH pre-ekstraksie van 69.1% xilaan (droë massa) uit suikerriet bagasse (SCB) het ‘n hoër natriumantrakinoon, gesifte pulpopbrengs gelewer (45.0%) met ‘n verbeterde afname in kappa-getal (15.5) en uitstekende skeursterkte sonder verlaging in viskositeit, soos vergelyk met nie-ge-ekstraheerde suikkerrietbagasse. Daarteenoor het die resultate verkry met die geoptimeerde verdunde swawelsuur preekstraksie van al die getoetste rumateriale getoon om‘n negatiewe effek te gehad het op die daaropvolgende kraft- of natriumantrakinoonverpulping dws het laer pulpopbrengste en swakker sterkte-eienskappe opgelewer. Die verskille was nietemin kleiner toe natriumantrakinoonverpulping ipv kraftverpulping gebruik is. Antrakinoon beskerm die koolhidrate teen die afskilreaksie in alkaliese medium. Daarteenoor het pre-ekstraksie van suikerrierbagasse met warm water tot 'n lae hoeveelheid (5.7%) xilaanoligomere gelei, terwyl die daaropvolgende natriumantrakinoonverpulping geen verlaging in pulpopbrengs veroorsaak het nie. Skeursterkte en optiese helderheid van handvelle wat uit warm water ge-ekstraheerde suikerrietbagasse vervaardig is, het ietwat verbeter terwyl breek-, trek- en barssterkte dieselfde was as van suikerrietbagasse pulp wat nie ge-ekstraheer is nie. Net so belangrik was die waargenome hoër skeur- en barsindekse van handvelle vervaardig van reuse bamboes in vergelyking met E. grandis van beide geekstraheerde en nie ge-ekstraheerde materiale voorberei onder dieselfde verpulpings toestande. Bamboes se sterker eienskappe was as gevolg van die hoër vesellengte en ander morfologiese eienskappe as diévan loofhout. Pulp wat vervaardig is van reuse bamboes het ‘n hoër kappanommer getoon as pulp van E. grandis as gevolg van die hoë kondensasiegedrag van bamboeslignien onder alkaliese toestande. Hoër kappanommers kon die gepaardgaande hoër aanvraag vir bleikchemikalieë verklaar. Ten slotte, die pulpmeul bio-raffinaderykonsep nl. deur hemisellulosesekstraksie met NaOH gekombineer met óf ‘n gemodifiseerde kraft verpulping óf ‘n gemodifiseerde natriumantrakinoon verpulping, is wel uitvoerbaar. Dit word egter sterk beïnvloed deur die tipe ru-materiaal en die ekstraksie-metode gebruik, asook deur die kwaliteits- en gebruiksvereistes van verskillende tipes papier. ‘n Lae aanvraag vir verpulpingschemikalieë, vergelykbare pulpopbrengste en die verbetering in fisies-chemiese eienskappe van pulp vanaf pre-ge-ekstraheerde materiale is waargeneem. Verder kon, as gevolg van xilaan ekstraksie, meer ge-ekstraheerde materiaal in die verteerder gelaai word as wanneer nie-ge-ekstraheerde materiaal gebruik is.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2010. / Thesis submitted in partial fulfilment of the requirements for the Degree of MASTER OF SCIENCE IN ENGINEERING (MINERAL PROCESSING) in the Department of Process Engineering at the University of Stellenbosch / ENGLISH ABSTRACT: The use of dimensional analysis to scale-up mechanically agitated flotation processes and to identify deficiencies in froth flotation plants was explored. The full range of operating variables was considered, such as particle size distribution, reagent suite, conditioning time, retention time, machine geometry, aeration, solids suspension, power requirements and turbulence. Dimensional analysis offers a methodology to combine variables into dimensionless groups to guide the scale-up process based on the notion of similarity. Ten dimensionless groups were developed and combined with metallurgical variables, such as liberation, reagents dosage and flow diagrams to produce a scale-up and evaluation tool, applicable to any mechanically agitated flotation process. In many hydrodynamic studies, the researchers considered hydrodynamic variables based on rotor diameter. In this case the hydrodynamic variables based on rotor diameter represent mechanism “ability”, while parameters based on cell diameter are considered “requirement”. Dimensionless groups have also been applied to the definition of basic parameters of the kinetic constant, such as floatability, bubble surface area flux and froth recovery factor. It also showed that the bubble surface area flux has a maximum with increased aeration, where similar models do not show this dependence. Analysis by computational fluid dynamics and Perspex modelling revealed valuable insight into the inner working of the Wemco flotation machine, such as air dispersion, turbulence levels, separation zones and solids concentration. Design changes to the rotor, disperser, hood and geometrical lay-out produced a marked improvement in flotation conditions. It also supported certain dimensionless numbers measured in full scale plants. Case studies confirmed that almost all flotation plants, irrespective of the minerals floated, suffer from the same deficiencies. Dimensional similitude offers a unique tool to identify these deficiencies and to predict the effect of recommended improvements. In almost every case where the fundamental requirement of similarity was applied, an improvement in performance was observed. Finally a new algorithm is proposed for the scale-up of flotation plants and the application is demonstrated in the design and testing of a pilot plant. / AFRIKAANSE OPSOMMING: Die gebruik van dimensionele analise in die opskaal van flottasieprosesse en die identifisering van flottasieaanlegprobleme is ondersoek. Die volle bereik van bedryfsveranderlikes is ondersoek, soos partikelgrootte, kondisioneringstyd, retensietyd, geometrie, lugvloei, suspensie van vastestowe, turbulensie en drywingsvereistes. Dimensielose analise is die proses waardeur veranderlikes deur wiskundige manipulasie gekombineer word in dimensielose groepe. Tien dimensielose groepe is ontwikkel en is tesame met metallurgiese veranderlikes soos vrystelling, reagensdosering en vloeidiagramme gekombineer om gebruik te word om gelykvormigheid te bewerkstellig. Hierdie proses is van toepassing op enige flottasieproses gebaseer op meganies geagiteerde toerusting. Dimensielose groepe is ook gebruik in die definisie en kwantifisering van turbulensie, agitasie, geometrie, suspensie van vastestowe, verspreiding van lug en drywingsvereistes. Daarbenewens is die groepe gebruik in die definisie van die basiese veranderlikes van die kinetiese konstante soos lugborreloppervlakvloed, suspensie, en herwinning in die skuimfase. Die groepe is ook gebruik in die bewys dat die lugborreloppervlakvloed ´n maksimum het met toename in lugvloei. In baie gevalle word hidrodinamiese veranderlikes uitgedruk in terme van die rotordiameter en in hierdie studie word dit beskou as meganisme “vermoë”. Die hidrodinamiese veranderlikes gebaseer op sel-diameter word beskou as “behoefte”. Berekeningsvloeidinamika en Perspex modellering het waardevolle insig verskaf in die binne-werking van die Wemco flottasiemasjien soos lugverspreiding, turbulensie en partikelkonsentrasie en is ook gebruik om sekere dimensielose getalle wat in volskaalse aanlegte gemeet is, te verifieer. Gevallestudies het bevestig dat feitlik alle flottasieaanlegte, ongeag die soort mineraal, gebuk gaan onder dieselfde afwykings. Dimensionele analise bied ‘n eenvoudige benadering om hierdie afwykings te identifiseer en om die effek van veranderings te voorspel. In alle gevalle waar die beginsels van gelykvormigheid slaafs gevolg is, het n merkbare verbetering in prestasie voorgekom. Ten slotte is ´n nuwe opskaleringsalgoritme ontwikkel en is die toepassing daarvan gedemonstreer deur die ontwerp en toets van ´n loodsaanleg, gebaseer op die Wemco geometrie.