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Simulating processes is a valuable tool which provides in-depth knowledge about overall performance of a system and caters valuable insight on improving processes. Current simulation models are developed and run based on the existing business and operations conditions at the time during which the simulation model is developed. Therefore a simulation run over one year will be based on operational and business conditions defined at the beginning of the run. The results of the simulation therefore are unrealistic, as the actual process will be going through dynamic changes during that given year. In essence the simulation model does not have the intelligence to modify itself based on the events occurring within the model. The paper presents a dynamic simulation modeling methodology which will reduce the variation between the simulation model results and actual system performance. The methodology will be based on developing a list of critical events in the simulation model that requires a decision. An expert system is created that allows a decision to be made for the critical event and then changes the simulation parameters. A dynamic simulation model is presented that updates itself based on the dynamics of the actual system to reflect correctly the impact of organization restructuring to overall organizational performance.

Biodiesel has achieved worldwide recognition for many years due to its renewability, lubricating property, and environmental benefits. The abstract represents a summary of all the chapters of the thesis. The research chapters are defined as research phases in the abstract. The thesis starts with an introduction followed by literature review. In the literature review, all the necessary data were collected reviewing the literature. Then an artificial neural network model (ANN) was built based on the published research data to capture the general trends or to make predictions. Both catalyst properties and reaction conditions were trended and predicted using the network model. The review study revealed that esterification and transesterification required catalysts with slightly different properties. In the first phase of the study, biodiesel production using 12-Tungstophosphric acid (TPA) supported on SBA-15 as a solid acid catalyst was studied. In this phase of the study, a large number of 0-35% TPA on SBA-15 catalysts were synthesized by impregnation method and the effects of various operating conditions such as–catalyst wt.% and methanol to oil molar ratio on the transesterification of model feedstock Triolein were studied. A 25% TPA loading was found to be the optimum. A 4.15 wt.% catalysts (based on Triolein) and 39:1 methanol to Triolein molar ratio was found to be the optimum reaction parameter combination, when the reaction temperature was kept fixed at 200C, stirring speed of 600 rpm and 10 h reaction time. The biodiesel yield obtained using this condition was 97.2%. In the second phase of the study, a 12-Tungstophosphoric acid (TPA) was supported by using organic functional group (i.e. 3-aminopropyltriethoxysilane (APTES)) and was incorporated into the SBA-15 structure. A 45 wt.% TPA incorporated SBA-15 produced an ester with biodiesel yield of 97.3 wt.%, when 3 wt.% catalyst (based on the green seed canola (GSC) oil) and 25.8:1 methanol GSC oil molar ratio were used at 2000C for reaction time of 6.2 h. In the third phase, process sustainability (i.e. process economics, process safety, energy efficiency, environmental impact assessment) studies were conducted based on the results obtained in phase three. Based on the study, it was concluded that heterogeneous acid catalyzed process had higher profitability as compared to the homogeneous acid catalyzed process. Additionally, it was obtained that heterogeneous acid catalyzed process was safe, more energy efficient and more environment friendly than homogenous process. In the fourth phase, the catalytic activity of Tungsten oxide (WO3) and TPA supported (by impregnation) on H-Y, H-β and H-ZSM-5 zeolite catalysts were tested for biodiesel production from Green Seed Canola (GSC) oil. In this phase iii of the study, TPA/H-Y and TPA/H- zeolite were proved to be effective catalysts for esterification and transesterification, respectively. A 55% TPA/H- showed balanced catalytic activity for both esterification and transesterification. It yielded 99.3 wt.% ester, when 3.3 wt.% catalyst (based on GSC oil) and 21.3:1 methanol to GSC oil molar ratio were used at 200C, reaction pressure of 4.14 MPa and reaction time of 6.5 h. Additionally, this catalyst (55% TPA/H-) was experimented for etherification of pure glycerol, and maximum conversion of glycerol (100%) was achieved in 5 h at 120C, 1 MPa, 1:5 molar ratio (glycerol: (tert-butanol) TBA), 2.5% (w/v) catalyst loading. Later, these conditions were used to produce glycerol ether successfully from the glycerol derived after transesterification of green seed canola oil. A mixture of GSC derived biodiesel, and glycerol ether was defined as biofuels. In the fifth phase, catalytic activity of H-Y supported TPA (using different impregnation methods) was studied in details further for esterification of free fatty acid (FFA) of GSC oil. From the optimization study, 97.2% FFA (present in the GSC oil) conversion was achieved using 13.3 wt.% catalyst, 26:1 methanol to FFA molar ratio at 120C reaction temperature and 7.5 h of reaction time. In the sixth- and final phase, techno-economic and ecological impacts were compared between biodiesel and combined biofuel production processes based on the results obtained in phase four. Based on the study, it was concluded that, biodiesel production process had higher profitability as compared to that for combined biofuel production process. Additionally, biodiesel production process was more energy efficient than combined biofuel production process. However, combined biofuel production process was more environment-friendly as compared to that for biodiesel production process.

Jatropha curcas L. is a drought-resistant plant which can be grown in poor soil and marginal lands. The use of Jatropha seed oil to produce biodiesel has been widely studied in recent years. Results showed that it is one of the most promising alternatives for conventional petro-diesel. Currently, hexane is still the most commonly used solvent for commercial oil extraction. However, the increasing price and flammability properties of hexane are motivating industry to seek alternative solvents. The objectives of this study are to design and analyze the Jatropha seed oil extraction for use in biodiesel production, and to provide a systematic safety-economic analysis of alternative solvents that can be used in Jatropha seed oil extraction. First, a base-case flowsheet is synthesized for oil extraction. Then, the base-case extraction process and each solvent Fire and Explosion Index (F & EI) and the Solvent Safety Index (SSI). Eight solvents, including n-heptane, toluene, xylene, dichloromethane, chloroform, 1,2-dichloroethane, methanol and ethanol are selected for candidates by comparing these results to those for hexane. Two cases are developed to evaluate the economic potential of these candidates. Furthermore, heat integration is applied to the process to minimize energy usage. Finally, a comprehensive solvent comparison is developed based on F & EI, SSI, solvent makeup cost, utilities cost, and capital investment. The results show that chloroform is the optimal solvent, while dichloromethane is the next best.

In this study, the implementation of membrane technology at Anglo Platinum’s base metals refinery to separate acid from metal containing solutions was investigated. The refinery includes a circuit known as the “sulphur removal section”, where the acid in the spent nickel electrolyte is neutralized with caustic soda to remove the excess sulphur from the overall process. Reagent costs associated with acid neutralisation, result in high operating expenditures. An alternative process route is required to improve efficiencies and stay competitive. Nanofiltration was investigated to separate acid from nickel, with the aim of recovering the acid and thereby reducing the need for expensive neutralisation. The objectives of this study were twofold: (1) investigate and simulate the current base metals refinery, and (2) use the understanding and process know-how to investigate the use of nanofiltration by modifying the simulation to include for this technology. The modified process simulation was then used to evaluate the type of membrane required for technical viability. The process investigation of the refinery proceeded with literature studies done on base metals recovery process, chemical reactions and design criteria applicable to the process. A simulation of the base metals refinery was undertaken in Aspen Plus using the information established in the process investigation. The simulation provided insight into the operational issues across the flowsheet, and identified key areas of the process which were sensitive to parameter changes in the sulphur removal section. Areas which were impacted were the electrowinning and copper removal section. The simulation therefore provided a useful tool to predict process variabilities as a result of plant modifications. The investigation into nanofiltration found that it can successfully be used to separate metal ions from acid, subject to the constraints of metal ion concentrations. Pre-treatment of the nickel spent electrolyte was required to remove most of the sodium sulphate in solution, since this can cause fouling and thereby degrade membrane performance. For this reason, a cold crystallization process was introduced for the removal of sodium sulphate. However the sodium removal process caused the sodium sulphate levels in the electrowinning feed to drop below 100 g/l. Therefore minor modifications had to be made to the electrowinning pre-treatment process. The nanofiltration process itself consisted of a series of six nanofiltration stages with dilution of the interstage feed to allow the system to operate below osmotic pressure and wash out all the acid from the system. The modified simulation including the new sulphur removal circuit (nanofiltration process) was completed by integrating the current base metals refinery simulation with the new sulphur removal process, thereby providing a tool where different membrane characteristics could be varied to enable the performance of the overall process to be evaluated. The membrane parameters varied were the nickel rejection, the sodium rejection and the acid rejection. The simulation predicted that each of the cases which varied the mentioned parameters would be technically feasible, although not necessarily economically feasible. The process was most sensitive to acid rejection. The key variables were the amount of water used for dilution, and the membrane size. An exponential distribution was present for the sensitivity of membrane size versus acid rejection; thus realistic membrane sizes can only be achieved if the acid rejection is -100% or less. Furthermore, the addition of dilution water results in the nickel being washed out with the acid, despite nickel rejection being in the region of 99.5%. This demonstrates the importance of the membrane nickel rejection to be as high as possible. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2014

In this study, the implementation of membrane technology at Anglo Platinum’s base metals refinery to separate acid from metal containing solutions was investigated. The refinery includes a circuit known as the “sulphur removal section”, where the acid in the spent nickel electrolyte is neutralized with caustic soda to remove the excess sulphur from the overall process. Reagent costs associated with acid neutralisation, result in high operating expenditures. An alternative process route is required to improve efficiencies and stay competitive. Nanofiltration was investigated to separate acid from nickel, with the aim of recovering the acid and thereby reducing the need for expensive neutralisation. The objectives of this study were twofold: (1) investigate and simulate the current base metals refinery, and (2) use the understanding and process know-how to investigate the use of nanofiltration by modifying the simulation to include for this technology. The modified process simulation was then used to evaluate the type of membrane required for technical viability. The process investigation of the refinery proceeded with literature studies done on base metals recovery process, chemical reactions and design criteria applicable to the process. A simulation of the base metals refinery was undertaken in Aspen Plus using the information established in the process investigation. The simulation provided insight into the operational issues across the flowsheet, and identified key areas of the process which were sensitive to parameter changes in the sulphur removal section. Areas which were impacted were the electrowinning and copper removal section. The simulation therefore provided a useful tool to predict process variabilities as a result of plant modifications. The investigation into nanofiltration found that it can successfully be used to separate metal ions from acid, subject to the constraints of metal ion concentrations. Pre-treatment of the nickel spent electrolyte was required to remove most of the sodium sulphate in solution, since this can cause fouling and thereby degrade membrane performance. For this reason, a cold crystallization process was introduced for the removal of sodium sulphate. However the sodium removal process caused the sodium sulphate levels in the electrowinning feed to drop below 100 g/l. Therefore minor modifications had to be made to the electrowinning pre-treatment process. The nanofiltration process itself consisted of a series of six nanofiltration stages with dilution of the interstage feed to allow the system to operate below osmotic pressure and wash out all the acid from the system. The modified simulation including the new sulphur removal circuit (nanofiltration process) was completed by integrating the current base metals refinery simulation with the new sulphur removal process, thereby providing a tool where different membrane characteristics could be varied to enable the performance of the overall process to be evaluated. The membrane parameters varied were the nickel rejection, the sodium rejection and the acid rejection. The simulation predicted that each of the cases which varied the mentioned parameters would be technically feasible, although not necessarily economically feasible. The process was most sensitive to acid rejection. The key variables were the amount of water used for dilution, and the membrane size. An exponential distribution was present for the sensitivity of membrane size versus acid rejection; thus realistic membrane sizes can only be achieved if the acid rejection is -100% or less. Furthermore, the addition of dilution water results in the nickel being washed out with the acid, despite nickel rejection being in the region of 99.5%. This demonstrates the importance of the membrane nickel rejection to be as high as possible. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2014

Mudança climática é um processo global, real e inequívoco. Para sua mitigação, a substituição de combustíveis fósseis por energias renováveis está sendo cada vez mais empregada. Devido à rápida velocidade de crescimento das microalgas, seu cultivo é visto como uma das alternativas mais promissoras para a produção de biocombustíveis. No presente trabalho, foi elaborado um modelo matemático fenomenológico que descreve o crescimento da microalga Chlorella vulgaris. Este modelo foi validado através de experimentos realizados em um reator piloto com capacidade de 1000 L tipo \"open pond\" (reator de raias) aberto ao ambiente, em condições não-axênicas. A variação de concentração devida à evaporação e/ou adição de água foi levada em conta no modelo. O modelo matemático desenvolvido, contendo dois parâmetros ajustáveis, descreve a variação da concentração de biomassa em função do tempo sob condições variáveis de luminosidade e temperatura. Os parâmetros ajustáveis são q (constante para conversão de intensidade luminosa em crescimento fotossintético, em klux-1 min-1) e Imax (limite máximo de intensidade luminosa, em klux). Previamente ao projeto do reator, foram realizados experimentos em reator de laboratório (utilizando a metodologia Taguchi) com o objetivo de determinar quais os fatores mais críticos para o crescimento da espécie de microalga selecionada e que, por isso, deveriam ser controlados com maior precisão. Além disso, foi analisada teoricamente a relevância da consideração do transporte de massa de CO2 no processo. Como este transporte é muito mais lento, a resistência controladora do processo é o crescimento fotossintético. Após a construção do reator piloto, foram realizados dois experimentos preliminares (os quais serviram para aperfeiçoar o aparato e o procedimento experimental) e três experimentos definitivos, registrando-se dados ambientais (temperatura, intensidade luminosa e pH) e de concentração ao longo do tempo. Utilizando os dados de temperatura e luminosidade em função do tempo como entrada, os parâmetros q e Imax otimizados foram ajustados às curvas de concentração versus tempo de cada experimento. Para tal foram desenvolvidos programas de integração de equações diferenciais e de otimização escritos em ambiente Scilab®. Verificou-se que, apesar da variabilidade devida às condições ambientais dos experimentos, obteve-se boa aderência dos dados simulados aos experimentais. Uma análise estatística dos parâmetros q e Imax calculados em cada experimento forneceu coeficientes de variação para estes parâmetros de 17 % e 5 %, respectivamente. Concluiu-se, portanto, que o modelo matemático desenvolvido neste trabalho pode ser empregado para prever o desempenho de um reator de raias em condições ambientais variáveis, bastando para isto o ajuste de dois parâmetros. / Mudança climática é um processo global, real e inequívoco. Para sua mitigação, a substituição de combustíveis fósseis por energias renováveis está sendo cada vez mais empregada. Devido à rápida velocidade de crescimento das microalgas, seu cultivo é visto como uma das alternativas mais promissoras para a produção de biocombustíveis. No presente trabalho, foi elaborado um modelo matemático fenomenológico que descreve o crescimento da microalga Chlorella vulgaris. Este modelo foi validado através de experimentos realizados em um reator piloto com capacidade de 1000 L tipo \"open pond\" (reator de raias) aberto ao ambiente, em condições não-axênicas. A variação de concentração devida à evaporação e/ou adição de água foi levada em conta no modelo. O modelo matemático desenvolvido, contendo dois parâmetros ajustáveis, descreve a variação da concentração de biomassa em função do tempo sob condições variáveis de luminosidade e temperatura. Os parâmetros ajustáveis são q (constante para conversão de intensidade luminosa em crescimento fotossintético, em klux-1 min-1) e Imax (limite máximo de intensidade luminosa, em klux). Previamente ao projeto do reator, foram realizados experimentos em reator de laboratório (utilizando a metodologia Taguchi) com o objetivo de determinar quais os fatores mais críticos para o crescimento da espécie de microalga selecionada e que, por isso, deveriam ser controlados com maior precisão. Além disso, foi analisada teoricamente a relevância da consideração do transporte de massa de CO2 no processo. Como este transporte é muito mais lento, a resistência controladora do processo é o crescimento fotossintético. Após a construção do reator piloto, foram realizados dois experimentos preliminares (os quais serviram para aperfeiçoar o aparato e o procedimento experimental) e três experimentos definitivos, registrando-se dados ambientais (temperatura, intensidade luminosa e pH) e de concentração ao longo do tempo. Utilizando os dados de temperatura e luminosidade em função do tempo como entrada, os parâmetros q e Imax otimizados foram ajustados às curvas de concentração versus tempo de cada experimento. Para tal foram desenvolvidos programas de integração de equações diferenciais e de otimização escritos em ambiente Scilab®. Verificou-se que, apesar da variabilidade devida às condições ambientais dos experimentos, obteve-se boa aderência dos dados simulados aos experimentais. Uma análise estatística dos parâmetros q e Imax calculados em cada experimento forneceu coeficientes de variação para estes parâmetros de 17 % e 5 %, respectivamente. Concluiu-se, portanto, que o modelo matemático desenvolvido neste trabalho pode ser empregado para prever o desempenho de um reator de raias em condições ambientais variáveis, bastando para isto o ajuste de dois parâmetros.

The diploma thesis deals with using discrete event simulation as a tool for supporting decision-making process in the company with usage of simulation software Plant Simulation. This work briefly introduces business process modeling and simulation problems. In the diploma thesis there two varieties two varieties of supplying parts, compared with each other in a process view and there is a particular proposal solution, including the economical evaluation.

Although stereolithography (SL) is a remarkable improvement over conventional prototyping production, it is being pushed aggressively for improvements in both speed and resolution. However, it is not clear currently how these two features can be improved simultaneously and what the limits are for such optimization. In order to address this issue a quantitative SL cure process model is developed which takes into account all the sub-processes involved in SL: exposure, photoinitiation, photopolymerizaion, mass and heat transfer. To parameterize the model, the thermal and physical properties of a model compound system, ethoxylated (4) pentaerythritol tetraacrylate (E4PETeA) with 2,2-dimethoxy-2-phenylacetophenone (DMPA) as initiator, are determined. The free radical photopolymerization kinetics is also characterized by differential photocalorimetry (DPC) and a comprehensive kinetic model parameterized for the model material. The SL process model is then solved using the finite element method in the software package, FEMLAB, and validated by the capability of predicting fabricated part dimensions. The SL cure process model, also referred to as the degree of cure (DOC) threshold model, simulates the cure behavior during the SL fabrication process, and provides insight into the part building mechanisms. It predicts the cured part dimension within 25% error, while the prediction error of the exposure threshold model currently utilized in SL industry is up to 50%. The DOC threshold model has been used to investigate the effects of material and process parameters on the SL performance properties, such as resolution, speed, maximum temperature rise in the resin bath, and maximum DOC of the green part. The effective factors are identified and parameter optimization is performed, which also provides guidelines for SL material development as well as process and laser improvement.

Paskutinį dešimtmetį bendrovės labai daug dėmesio skiria procesų analizei, veiklos efektyvumo didinimui. Verslo procesų valdymas pritraukia vis didesnį bendrovių dėmesį ir šis dėmesys joms leidžia pereiti nuo imituojamų verslo procesų prie realiai veikiančių. Verslo procesų valdymas apima procesų konstravimą, atvaizdavimą, kontrolę ir analizę. Bendrovės didina darbo efektyvumą nuolatos vertindamos procesų pridedamąją vertę. Verslo procesų tobulinimas yra nenutrūkstamas ciklas, kuriame itin svarbią rolę atlieka procesų konstravimas ir pertvarkymas. Yra begalės būdų pakeisti vystančius procesus ir tik geriausios alternatyvos procesas turi pakeisti realiai vykdomą. Intuityvus proceso pasirinkimas gali nemaloniai nustebinti ir sumažinti verslo efektyvumą vietoje siektų tikslų. Procesų imitavimas yra vienas iš tinkamų būdų jų pertvarkymui. Verslo procesų imitavimas padeda suprasti, analizuoti ir konstruoti procesus. Pasitelkus imitavimą procesai gali būti įvertinti ir palyginti. Imitavimas suteikia proceso poveikio verslo efektyvumui kiekybinį įvertinimą, pagal kurį lengva pasirinkti tinkamiausią procesą. Galima išskirti eilę žingsnių susijusių su verslo procesų imitavimu. Pirmiausia verslo procesas yra atvaizduojamas procesų modelyje. Tada identifikuojami po-procesai ir įvykiai. Yra apibrėžiama proceso eiga, nustatomos jo esybės ir nustatomi ryšiai tarp skirtingų proceso dalių. Galiausiai yra numatomi ir paskiriami resursai. Proceso modelis turėtų būti patvirtintas tik įsitikinus... [toliau žr. visą tekstą] / Business process is: “A collection of related, structured activities – a chain of events- that produce a specific service or product for a particular customer or customers” [How06]. A simulation is an imitation of some real thing, state of affairs, or process. The supporting tools of process mapping and business process simulation are used in the change process and assist in communicating the current process design and people's roles in the overall performance of that design. The simulation model is also used to predict the performance of new designs incorporating the use of information technology. The approach is seen to have a number of advantages in the context of a public sector organization. These include the ability for personnel to move from a traditional grouping of staff in occupational groups with relationships defined by reporting requirements to a view of their role in a process, which delivers a performance to a customer. By running the simulation through time it is also possible to gauge how changes at an operational level can lead to the meeting of strategic targets over time. Business processes are increasingly recognized as the key to competitive survival. The important opportunities inherent to this invisible economic asset are the foundations of process-centered management. Simulation of business processes creates added value in understanding, analyzing and designing processes by introducing dynamic aspects. It provides decision support by anticipation of... [to full text]