Masters Degrees (Chemical Engineering)

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Adaptive dynamic matrix control for a multivariable training plant.
(2001) Guiamba, Isabel Remigio Ferrao.; Mulholland, Michael.
Dynamic Matrix Control (DMC) has proven to be a powerful tool for optimal regulation of chemical processes under constrained conditions. The internal model of this predictive controller is based on step response measurements at an average operating point. As the process moves away from this point, however, control becomes sub-optimal due to process non-linearity. If DMC is made adaptive, it can be expected to perform well even in the presence of uncertainties, non-linearities and time-vary ing process parameters. This project examines modelling and control issues for a complex multivariable industrial operator training plant, and develops and applies a method for adapting the controller on-line to account for non-linearity. A two-input/two-output sub-system of the Training Plant was considered. A special technique had to be developed to deal with the integrating nature of this system - that is, its production of ramp outputs for step inputs. The project included the commissioning of the process equipment and the addition of instrumentation and interfacing to a SCADA system which has been developed in the School of Chemical Engineering.
Adsorption of heavy metals on marine algae.
(2005) Mbhele, Njabulo.; Carsky, Milan.; Pienaar, D. H.
Biosorption is a property of certain type of inactive, microbial biomass to bind and concentrate heavy metals from even very dilute aqueous solutions. Biomass exhibits this property, acting just as a chemical substance, as an ion exchanger of biological origin. It is particularly the cell wall structure of certain algae that is found responsible for this phenomenon. In these experiments, the rate and extent for removal of copper is subjected to parameters such as pH, initial metal concentration, biosorbent size, contact time, temperature and the ability of the biomass to be regenerated in sorption-desorption experiments. The metal adsorption was found to be rapid within 25 minutes. The maximum copper uptake of 30 mg of copper / g of biomass has been observed, in the following conditions: 100 mg / L, 0.1 g of biomass, pH 4 and at temperature of 25°C. From this study, it was found that copper uptake is increasing with increase in pH, with optimum being pH 4. Copper uptake increases substantially from 0 to 25 minutes. Metal biosorption behaviour of raw seaweed Sargassum in six consecutive sorptiondesorption cycles were also investigated in a packed-bed column, during a continuous removal of copper from a 35 mg/l aqueous solution at pH 4. The sorption and desorption was carried out for an average of 85 and 15 hours, respectively, representing more than 40 days of continuous use of the biosorbent. The weight loss ofbiomass after this time was 13.5%. The column service time decreased from 25 hrs in the first cycle to 10 hrs for the last cycle.
Adsorption studies for the separation of light hydrocarbons.
(2014) Govender, Inbanathan.; Ramjugernath, Deresh.; Naidoo, Paramespri.; Nelson, Wayne Michael.
Traditionally, the separation of ethylene from ethane is undertaken using a fractionation sequence. The distillation is performed at low temperatures and elevated pressures in conventional trayed fractionators. For economic feasibility, the separation scheme must be heat integrated to produce the low temperatures needed for separation – as low as 243 K. Low temperature distillation units are expensive to build and are typically only economically feasible for feed streams containing high amounts of ethylene. Adsorption provides a favourable alternative to the traditional low temperature distillation process. The availability of accurately measured adsorption data over a wide range of temperatures and pressures is vital in the design of efficient separation processes. However, reproducible binary adsorption data are not readily available in the literature due largely to the uncertainties involved in measuring adsorption equilibria. This project involved the measurement of adsorption equilibria using two techniques – the gravimetric and the volumetric technique. Particular focus was placed on the design and commissioning of a volumetric apparatus capable of measuring binary adsorption equilibria over a range of temperatures and pressures. The gravimetric apparatus is not capable of measuring multicomponent adsorption equilibria. The Thermodynamic Research Unit (TRU) has extensive capabilities in the field of phase equilibria with specialized expertise in the field of vapour liquid equilibria (VLE). The objective of this project is to develop competence in the field of adsorption equilibria by designing and commissioning new apparatus. This forms part of a larger objective to extend the capabilities of TRU. The volumetric apparatus designed and commissioned in this study uses an innovative gas mixer to prepare binary mixtures for adsorption equilibrium measurements. The measured data were compared to literature to validate the measurement reproducibility of the apparatus and accuracy of measurement techniques used. Adsorption equilibrium data were measured for pure components and a binary system. Pure component adsorption data were measured for methane, ethane and ethylene. The binary system of ethane + ethylene was also investigated. Measurements were performed at pressures up to 15 bar, at temperatures of 298 K and 323 K, on an adsorbent zeolite 13X. The gravimetric and volumetric apparatus both showed good reliability and reproducibility. Uncertainties in temperature and pressure were 0.1 K and 4×10-3 bar for the gravimetric apparatus and 0.03 K and 0.002 bar for the volumetric apparatus respectively. The measured equilibrium data were fitted to the Langmuir, Sips and Vacancy Solution Model (VSM) adsorption models. The regressed parameters were used to predict binary adsorption equilibria. The Langmuir model performed the poorest across the pressure range investigated, with an average absolute deviation (AAD) as high as 5%. The deviation however, was comparable with the experimental uncertainties reported in literature. The Sips model improved upon the Langmuir model with the VSM model generally performing the best with an AAD of approximately 1%. The Extended Langmuir, Extended Sips and VSM all provided good predictions of the binary adsorption equilibria. The Extended Langmuir model performed best with an AAD of 3%. The Extended Sips model performed marginally poorer with an AAD of 3.05%. The VSM model performed satisfactorily with an AAD of 6%, marginally higher than the reported experimental uncertainties of 5%.
The anaerobic baffled reactor for sanitation in dense peri-urban settlements.
(2005) Mtembu, Dela Zama
Human consumption of water contaminated with faecal polIutants is the source of most sanitation related diseases. Excreta related diseases can be controlIed by improvements in excreta disposal. The primary consideration is to remove contact between the people and the faecal matter. The conventional waterborne sewage system is not an achievable minimum standard in dense peri-urban areas in the short term, due to its high cost. A need for a cost effective system that is easily maintained and does not require electricity or highly skilled labour for developing communities in South Africa was identified. The objective of this investigation was to assess the suitability of the Anaerobic Baffled reactor (ABR) as a primary onsite treatment system for low-income communities. The ABR is a high-rate compartmentalised anaerobic bioreactor, the design of which promotes the spatial separation of microorganisms. The trials were conducted on a 3200 L pilot-scale reactor placed at Kingsburgh wastewater treatment works, which receives only domestic wastewater. The ABR proved to be stable and consistent in its performance. Operating at a hydraulic retention time of 22.5 h, the reactor effiuent was ca. 200 mgCODIL. The 0,45flm filtered (soluble) COD was 100 mgIL, indicating there was approximately 100 mgIL of COD in the effluent that was in particulate form. The ABR achieved 60%VSS and 50%TSS removal with effiuent TSS content of about 225 mgIL. The system was hydraulicalIy overloaded and organicalIy under loaded. The Biochemical Methane Potential tests showed that 60% of the COD in the effiuent was biodegradable, and the effluent COD could be reduced to less than 100 mgCODIL if the HRT is increased giving a possible removal of 80%. The analytical campaign revealed that we were sampling at peak flow, when COD was high. The average COD fed to the reactor was much lower than that showed by routine analysis and the ABR had a "true" COD removal of 42%. The reactor was able to handle the daily variation ofthe wastewater. Settling tests were done to measure how much of the suspended solids in the ABR are retained at the operating upflow velocity. The method selected was shown to have an error that ranged from 5 to 42%, and the ABR was retaining between 60 and 90% ofsolids in the reactor at an upflow velocity of O.5m/h. The preliminary work with the fabric membrane showed great potential benefits that can be gained if it had to be included. It showed good ability to remove indicator organism and solids that contributed a lot to the effiuent COD. The membrane had 5 log removal of indicator organism and 80% reduction of COD. The membrane was operated for a short time before clogging; its operational lifespan needs to be greatly extended before it can be used with the reactor in a community. Since there is no nutrient removal in the AER, the effiuent can be used for food production provided sufficient pathogens removal is achieved. Provided that the first compartment can be modified and the concentration of pathogens in the effluent is sufficiently reduced, the ABR can be considered for use in a community.
An analysis and control of volatile organic Compound (VOC) emissions from petroleum storage tanks.
(2022) Naidoo, Theasha.; Moodley, Kuveneshan.; Naidoo, Prathieka.
Climate change is a growing phenomenon with its effects becoming more prominent to life on earth. According to the latest report by the Intergovernmental Panel on Climate Change (IPCC), some of the effects of climate change are irreversible. However, the implementation of large-scale reduction strategies on emissions may limit climate change over the long-term and provide short term air quality benefits. Petrochemical industries are a major contributor of Volatile Organic Compound (VOC) emissions as the need for storage facilities are expanding to accommodate for the increase in demand of organic liquids storage capacity. The Durban South Basin is a major industrial hub consisting of South Africa’s largest capacity oil refinery (SAPREF) and Engen refinery, soon-to-be tank terminal, located near a residential area. Therefore, the implementation of emission monitoring and reduction strategies are critical in ensuring climate resilience and the health and well-being of residents living within close proximity to the refineries. While there has been some progress in addressing climate change, emission data indicates that storage tanks contribute 42% of VOC emissions to total emissions from oil refineries. Due to limited studies conducted, there is a gap in the knowledge and understanding of proper monitoring and control practices of VOC emissions from petroleum storage tanks in Durban, South Africa. Therefore, the aim of this study is to provide strategies for implementation, such as simulation modelling using Aspen Plus ® and recommended process conditions, to achieve safe control and handling of emissions and to perform an Environmental Impact Assessment (EIA) for analyses of its potential effect on the environment and health of communities. Estimation of VOC emissions for crude oil and petroleum products (Ultra-Low Sulphur Diesel (ULSD), Unleaded Petrol 95 (ULP 95), Jet Fuel (JET A1) and Marine Gas Oil (MGO) were based on the AP-42 method, Aspen Plus ® simulations, manual flash calculations according to the Rachford-Rice iterative method and empirical correlations (such as the Vasquez-Beggs and Valko-McCain empirical correlation methods). The effects of atmospheric conditions, tank roof type, type of stored organic liquid and varying parameters (such as temperature, pressure and feed flowrate) on the VOC emissions from petroleum storage tanks were assessed to determine the most suitable monitoring method. The potential effect of Nitrogen blanketing (using the API 2000 7th ed. Standards) and Vapour Treatment on the reduction of VOC emissions from petroleum storage tanks were studied to determine its effectiveness as a control method. This study found that the Aspen Plus ® simulation method is an effective tool in monitoring VOC flashing emissions due to its reliability from its repeatability with the estimation crude oil test system in which the Aspen Plus ® and literature VOC measurement was consistent. Its ability to account for variations using the thermodynamic property models (Soave-Redlich-Kwong (SRK) for crude oil and Peng-Robinson (PENG-ROB)) for the product mixtures) further justifies the use of Aspen Plus ® as an effective monitoring method. Manual flash calculations under-estimated emissions across the organic mixture systems due to its less rigorous approach as it uses simplified equations which includes estimates of process conditions whereas Aspen Plus ® is able to account for variations is process conditions. The estimates determined using empirical correlations were mostly invalid due to the limited appliable range. All mixtures indicated a significant reduction in working and breathing losses when stored in an Internal Floating Roof Tank (IFRT) compared to a Floating Roof Tank (FRT). However, MGO was the exception. It was observed that these tanks should operate at 90 % capacity, with turnovers of 0 – 10 per year and a white painted shell, to ensure minimum emissions. Optimal operating tank temperatures should be maintained at 293.15 – 303.15 K and at pressures below 91 kPa. The installation of vapour recovery units is recommended for FRTs, and these measures are 90 % efficient. Due to the high API gravity of the ULP 95 mixture, the ULP 95 mixture should be targeted as a key mixture for control of VOC emissions as it has the potential to emit greater VOC emissions.
Analysis and experimental exploration of a nanofiltration membrane system, in the context of potential urine treatment processes.
(2014) Horstman, Donovan Edward.; Buckley, Christopher Andrew.; Santiago, Septien Stringel.
Abstract available in pdf file.
Analysis of an anaerobic baffled reactor treating complex particulate wastewater in an abr-membrane bioreactor unit.
(2010) Bwapwa, Joseph Kapuku.; Foxon, Katherine Maria.; Buckley, Christopher Andrew.
Providing water and proper sanitation to poor communities by 2015 is one of the United Nations targets for this millennium. In South Africa many communities aspire to waterborne sanitation. However, there is a technology gap for decentralized and sustainable waterborne sanitation systems capable of treating domestic wastewater (Foxon et al., 2006). Although domestic wastewater is more commonly treated using aerobic processes, anaerobic processes may be more appropriate for decentralized applications since they do not require aeration. Research is currently being undertaken to understand the behavior of a combined ABR-MBR unit for treating domestic wastewater. In this study, the anaerobic baffled reactor (ABR) was investigated by analyzing physico-chemical and biochemical data from experiments on a laboratory-scale ABR. This anaerobic reactor was treating complex particulate wastewater made up of sludge from the ventilated improved pit latrine toilets (known as VIP sludge). The main focus of this study was to establish the relationship between the increasing organic loading rates and the effluent characteristics (such as chemical oxygen demand: COD and extrapolymeric substances: EPS). The present work was structured in two parts; in the first part the reactor was operated at constant hydraulic retention time (HRT) without controlling feed characteristics. In the second part, the ABR was operated with step increases in organic loading rates. It was logistically not possible to provide a feed of real domestic wastewater to the laboratory-scale equipment. Consequently, a pit latrine sludge diluted with tap water was used to feed the ABR. This feed was found to have different biodegradability characteristics compared to domestic wastewater. However, the results still give insight into the performance of the ABR and into the treatability of VIP sludge. COD removal ranged from 52 to 80 % depending on the inlet COD. Some COD removal was due to solids retention in compartments, while it was estimated that only 28% of COD removal was due to biological degradation. Soluble extrapolymeric substances (proteins and carbohydrates) which are usually a by -product of anaerobic degradation were higher in the feed than in the effluent despite the increasing organic loading rates. However, more than 50 % of soluble extrapolymeric substances from the influent remained in the effluent and were found (in a parallel project) to influence membrane fouling in the membrane section of the experimental set-up (ABR-MBR unit). Parameters such as pH, conductivity, alkalinity, total and volatile solids were also investigated in this study. The pH decreased slightly from the inlet to the outlet during all runs even though the loading rates were increased. Conductivity increased significantly from influent to effluent with the increasing organic loading rates. Large amounts of total solids were retained in the reactor during the treatment process. Low alkalinity production was recorded during the operation of the reactor. In most cases, the data recorded in this study showed a low biological activity taking place while the reactor was working at room temperatures. Overall, up to 80% of removal efficiencies in terms of total COD and solids were recorded with increasing organic loading rates at constant hydraulic retention time. While these results do not allow the prediction of ABR-MBR performance during the treatment of real wastewater, it was concluded that: Most solids retention occurred in the feed tank. Most COD removal occurred as a result of solids retention and digestion. Loading characteristics did not strongly influence effluent EPS, pH or alkalinity, but did influence COD and conductivity. The relatively low biodegradability of the feedstock indicates that anaerobic digestion is not the most appropriate treatment for VIP sludge.
Analysis of nutrient requirements for the anaerobic digestion of Fischer-Tropsch reaction water.
(2013) Mathir, Aarefah.; Foxon, Katherine Maria.; Brouckaert, Christopher John.
Nutrients play an important role in the functioning of microorganisms during anaerobic digestion. The anaerobic treatment of industrial wastewaters, such as Fischer-Tropsch Reaction Water (FTRW), requires the addition of nutrients suitable for micro-organisms (micronutrients) since these wastewaters are devoid of essential metals. However, the dosing of nutrients is only effective if the metals are in a bioavailable form which in turn is dependent on the chemical speciation of the system. This study aimed to investigate and model the influence of precipitation on bioavailability by considering the extent to which precipitation can sequester metals into forms that are not bioavailable and the extent to which this sequestration can describe biological effects in an anaerobic system. Visual MINTEQ and Excel were used to develop a combined mass balance and chemical-equilibrium speciation model that considered the soluble and the precipitate metal phases. The model was compared to two sets of experimental analysis. Experiment A included metal analysis on the sludge and supernatant from glucose and ethanol fed ASBRs while Experiment B included similar analysis on FTRW fed ASBRs while biological parameters were monitored during a micro-metal washout experiment. Precipitation was found to sequester Al, Zn and Fe to a large extent making them non-bioavailable in Experiment A, while sulphide precipitates were predicted to dominate the metal speciation in Experiment B. In Experiment A, the organically bound metals phase was also a significant phase that sequestered metals. Furthermore, the rates of washout of most of the metals (excluding Mg) were over-predicted, which may have been due to the absence of other solid related phases in the model. This may also be attributed to kinetic effects in the system. Although there were reasonable correlations between the model predicted and the experimentally determined concentrations, it is recommended that the model should include the organically bound phase and consider mass transfer effects in the system. After 12 cycles without dosing micro-metals in Experiment B, the biogas production decreased by 43%. A decline in the predicted and determined soluble concentrations of a variety of metals were observed during this time, suggesting that there may be an agreement between predicted metals washout and reduction in anaerobic activity. Since the soluble metal concentrations did not decrease as rapidly as predicted by the model, a lag period between the two parameters was observed. Therefore, although the model provides an improved understanding of metal speciation and bioavailability such that recommendations may be made for prudent micro-metal dosing, further development is required for more accurate representations of the system.
Analysis of potential small satellite launch operations at the Denel Overberg test range.
(2022) Arunakirinathar, Aravind.; Pitot de la Beaujardiere, Jean-Francois Philippe.; Brooks, Michael John.
One of the primary objectives of the South African First Integrated Rocket Engine (SAFFIRE) programme of UKZN’s Aerospace System Research Group (ASReG) is to develop the capacity for orbital injection missions to Low Earth Orbits (LEOs) from South Africa. The most likely launch site for these missions is the Denel Overberg Test Range (OTR) near Cape Agulhas in the Western Cape. In order to determine the suitability of OTR as a launch site, it is imperative to gain an understanding of the performance, mechanics and structural loads of a vehicle entering orbit. The goal of this dissertation is to analyse the performance of a variety of modern two-stage launch vehicles as they travel along orbital injection trajectories into LEOs from OTR. This study considers solutions for the ascent-to-orbit trajectory for various launch vehicles. The primary method was to utilise trajectory optimisation methods and this was achieved by developing an optimal control solver, which makes use of direct Hermite-Simpson collocation methods, and a sequential quadratic programming solver. In order to improve the robustness and speed of the solver, formulae for the first order analytical derivative information of direct Hermite-Simpson collocation were developed. The optimal control solver was then validated using various linear and nonlinear examples from literature. The optimal control solver was used to analyse the performance of various hypothetical missions conducted by the following established launch vehicles: Rocket Lab’s Electron, SpaceX’s Falcon 1, SpaceX’s Falcon 9, and ASReG’s proposed small satellite launch vehicle, CLV. As a baseline comparison, all vehicles were launched from OTR into various LEOs. The payloads, trajectories, control histories and structural loads of these vehicles for injection were investigated. Finally, the effect of perigee altitude, inclination, and eccentricity of orbits on the extracted results was studied. The payload performance of the launch vehicles considered were relatively similar to that provided by each vehicle’s corresponding payload user guide. On all missions, the altitude of the Electron, Falcon 9 and CLV would constantly increase with range, however the Falcon 1 would tend to rise, dip, and then rise once more on missions to orbits with a perigee altitude of 200 km. Such trajectories are referred to as lofted trajectories and are common among vehicles with a low upper stage thrust to weight ratio (Patton and Hopkins, 2006), such as the Falcon 1. The tangent yaw and pitch of the thrust direction was highly linear for all analysed missions. This result allows for a reasonable control law which can be used to determine trajectory solutions using indirect optimal control methods. This study demonstrates the viability of the Denel Overberg Test Range as a competitive base of operation for space launch missions to LEO.
Application of a non-linear transformation to the surface fraction of the UNIQUAC model and the performance analysis of the subsequent model (FlexQUAC-Q).
(2007) Naidoo, Thishendren.; Ramjugernath, Deresh.
GE-model and equations of state are used to describe and predict phase equilibria. Current models have varying capabilities and some display selectivity for certain special mixtures. While many models are superior to others in their performance, all models share a common deficiency, the inability to simultaneously describe vapour-liquid (VLE) and liquid-liquid equilibria (LLE). Current models require separate parameters to describe the two equilibria. This formed the motivation for a non-linear transformation which was formulated by Rarey (2005). The transformation was applied to the concentration space. The clear advantage of such a transformation was that it could be easily applied to any model. The flexibility of the model was drastically increased. The effects were investigated on the local composition models, in particular the UNIQUAC model resulting in the FlexQUAC model. The model was used to regress a host of VLE and LLE data sets contained in the Dortmund Data Bank (DDB). The transformation had the desired effect on the flexibility of the model and the model was now able to describe VLE and LLE. However a symmetric transformation applied to the concentration space might not be effective in the description of systems exhibiting large difference in molecular size. This is a clear disadvantage of the proposed FlexQUAC model. In order to allow the model to cater to asymmetric systems, the transformation is now applied to the surface fraction of the residual contribution of the UNIQUAC model. The Guggenheim-Staverman expression in the combinatorial part was not transformed. Both the original combinatorial term and the more suitable modification of Weidlich and Gmehling (1987) were used. The newly formed model was called the FlexQUAC-Q model. The development of the FlexQUAC-Q model, derivation of activity coefficient expressions, model implementation and its performance analysis form the basis for this research study. The activity coefficient of the new model had to be re-derived due to the application of the transformation to the residual contribution of the UNIQUAC equation. The computation of the activity coefficient was programmed in FORTRAN and integrated into the regression tool (RECVAL) of the Dortmund Data Bank (DDB). The RECVAL tool was used to regress data sets contained in the DDB. Results obtained were comparable to those obtained using the GEQUAC model. The regression was also performed in EXCEL for the three models (UNIQUAC, FlexQUAC, FlexQUAC-Q). The regression in EXCEL was more rigorous and was used for the comparison of the objective functions and to obtain a set of unique model parameters for each data set. The performance of the FlexQUAC-Q model was assessed utilizing the same data sets used to analyse the performance of the FlexQUAC model. The model's performance was assessed in the regression of 4741 binary VLE data sets, 13 ternary VLE data sets and carefully select ternary LLE cases. The minor mean relative reduction of about 3% of the objective function using FlexQUAC-Q compared to FlexQUAC was observed compared to a reduction by about 53% relative to the UNIQUAC-results. It was necessary to illustrate that the new model does not degenerate the model's existing capabilities (e.g. ability to predict multi-component mixtures from binary data) and that the model performs as well as or superior to the UNIQUAC model. FlexQUAC-Q performed similarly to FlexQUAC. However the improvement in the qualitative description of data sets exhibiting asymmetry is apparent. Herein lies the justification of such a modification and this illustrates the preference of such a model when asymmetric systems are being considered. In addition, the FLEXQUAC-Q model can be adapted to be implemented into a group contribution method, a distinct advantage over the previous model FlexQUAC. The equations for the application of a non-linear transformation to a functional group activity coefficient model, UNIFAC are also explored in this study. The resulting model is referred to as FlexFaC.
Application of artificial neural networks as a predictive tool for the analysis of chemical engineering processes.
(2017) Khumalo, Siphesihle Praise-God.; Lokhat, David.
Abstract available in PDF file.
Application of graph theory to resource distribution policy-based synthesis of industrial symbiosis networks.
(2021) Dayal, Sidanth Bhawani.; Rawatlal, Randhir.
Industrial symbiosis (IS) involves the repurposing of waste and by-product streams from one chemical industry as feedstock to another. Given the growing environmental and economic concerns, it has become increasingly difficult for industries not to participate in IS. This has encouraged much research into the field, with IS network design being an important optimisation problem in the research space. However, challenges are associated with the creation of IS networks, with transportation costs and resource distribution being key factors. Furthermore, solution strategies are usually complex and neglect the structural features of the network. A possible solution is the use of graph theory for IS network creation. It was hypothesized that structural features of an IS network can evaluate the effect of distribution policies on IS networks created by graph matching algorithms. The Simplex method (SM), Edmonds-Karp algorithm (FF), and the Hungarian method (HM) were adapted to model IS networks, with the intention to establish a ranking in the suitability in creating IS networks. The adaption rendered the algorithms applicable to feasible IS network discovery under different distribution policies. This graph-based approach allowed for the seamless extraction of the network features as graph metrics. Rigorous testing of the adapted algorithms’ performance using graph metrics was done by simulating numerous IS scenarios. It was found that HM identified connections that, on average, minimised transportation costs to the greatest extent. The HM created networks with the smallest travelling distance than those of SM and FF, showing a 9 % and 6.06 % lower value than SM and FF, respectively. Furthermore, HM-IS networks created more stable and fair networks, which was inferred from the graph metrics. To confirm the HM’s apparent superiority in IS network creation, a case study was simulated with the defined distribution policies being modelled from the matching features. Each distribution policy was quantified as a cost from which it was found that HM-IS networks had a 72.5 % and 74.9 % lower overall distribution cost than FF-IS networks and SM-IS networks, respectively. It was concluded that HM is the most suited for IS network creation and that graph-based modelling of IS is a feasible approach.
Application of membrane filtration in system closure of white water systems in newsprint mills.
(2015) Naicker, Devi.; Sithole, Bishop Bruce.; Ntunka, Mbuyu Germain.
The pulp and paper industry is considered to be one of the most water intensive industries in S.A. With increasing environmental regulations and awareness the industry is leaning towards system closure. By recycling water and using it back in the process, the industry can considerably reduce its consumption of fresh water as well as its production of waste water. One method that is gaining momentum for the purification of water is membrane filtration. Membrane filtration does not require any sophisticated heat-generating equipment as compared to conventional separation methods like evaporation making it a viable choice. It is, however, prone to fouling and requires long membrane cleaning cycles. The first part of the study involved the simulation of system closure in the laboratory using a Rapid-Kothen sheet forming machine. This was conducted in order to determine the accumulation of the different contaminants as the white water is recycled. Results obtained indicate that the accumulation of contaminants with increasing number of cycles tends to exhibit a linear relationship. The burst index and brightness of the paper decreased as the level of closure increased. The main aim of the project was to evaluate ultrafiltration as the core process for purification of white water in terms of productivity, retention, flux decline, fouling and cleanability of the membrane as well as to determine the optimum operating conditions that reduce fouling. Polymer membranes having different molecular weight cut offs (10, 50, 100 and 150 kDa) were tested. Overall it was established that the 100 kDa membrane exhibited the lowest degree of irreversible fouling, the best cleanability, the highest productivity and average permeate flux and the permeate obtained from this membrane met most of the water quality requirements for the reuse of water in the paper manufacturing process. The 100 kDa membrane was used in further studies. The optimum operating conditions that reduce fouling was determined using the Taguchi method. Three parameters were investigated at three levels i.e. temperature (20, 40 and 60°C), pressure (1,2 and 3 bar) and volume reduction factor (VRF) (0.63, 0.71 and 0.86). Results obtained indicated that low temperatures, pressures and VRF values reduced the fouling hence the optimum operating conditions were a temperature of 20°C, a pressure of 1 bar and a VRF of 0.63. The permeate quality obtained at the optimum conditions is in accordance with the water quality standards for the reuse of water in the process. Alum and FeCl3 coagulation were used as pre-treatments to ultrafiltration to reduce the membrane fouling thereby increasing the membrane life. Results obtained indicate that twice as much FeCl3 than alum is required to obtain a similar reduction in suspended solids and turbidity and a low sludge volume index (SVI). FeCl3 is more expensive than Alum; requiring twice as much would considerably increase the cost of treatment. Hence alum was chosen as the coagulant to be used in further tests. It was found that the optimum dosage and pH were 288.8 mg/L and 7.68 respectively.
The application of non-thermal plasma-catalysis in Fischer-Tropsch synthesis at high pressure.
(2016) Govender, Byron Bradley.; Ramjugernath, Deresh.
Abstract available in PDF file.
Application of pinch technology in an integrated pulp and paper mill.
(2003) Naylor, Gladys M.; Brouckaert, Christopher John.
The objective of this investigation was to utilise water pinch analysis as a tool for the optimisation of fresh water use in an integrated pulp and paper mill. The investigation was carried out at Mondi Paper in Merebank, south of Durban. The pulp and paper manufacturing process is a large consumer of fresh water and minimising the amount of fresh water used in the processes is beneficial from both a cost and environmental point of view. There are examples of mills which have "closed" their water systems to the extent that fresh water make up is minimal and most of the water is recycled and reused in a closed loop. These examples provide guidance on the basis of proven methods for reducing water consumption in the pulp and paper industry and can be used as a reference for mills wishing to reduce water consumption by making use of tried and tested methods. This investigation sought to provide an alternative method to identifying potential savings in fresh water consumption by making use of water pinch analysis. This was done at Mondi Paper by analysing individual parts of the mill and then a larger section of the mill which included both pulp and paper production. Flow rates of water streams and fibre content in those streams were obtained from plant data, where available, and this data was used to produce.a mass balance using the Linnhoff-March software, Water Tracker. The balance produced using Water Tracker provided the missing flow and fibre content data and this data was used as the input for the Linnhoff-March software, Water Pinch , to perform the water pinch analysis. The results achieved when analysing the individual parts of the mill did not demonstrate potential for significant savings in fresh water consumption, however the analysis of the integrated section of the mill identified a potential reduction in fresh water. It was found that the application of a single contaminant analysis to the larger section of the mill identified a possible reduction in the freshwater requirement of 8.1% and a reduction in effluent generated of 5.4%. This is a savings of R1 548 593 per annum based on 2003 costs of fresh water and effluent disposal. This analysis was conducted using the most simplified representation possible to produce meaningful results in order to evaluate the effectiveness of water pinch analysis in optimising the fresh water consumption in an integrated pulp and paper mill. It is demonstrated that water pinch analysis is potentially a useful tool in determining the minimum fresh water requirement of a site.
Application of the truncated perturbed chain-polar statistical associating fluid theory (tPC-PSAFT) to alcohol/alkane mixtures at high pressures.
(2020) Hussain, Mishqah.; Moodley, Kuveneshan.
Constitutive equations, such as equations of state (EoS) characterize mathematical relationships between state functions under set physical conditions and are imperative for the accurate design of chemical processes (Devilliers, 2011; Al-Malah, 2015). Most models, however, fail to accurately predict thermophysical properties of complex mixtures such as those exhibiting molecular association and hydrogen bonding. The Statistical Associating Fluid Theory (SAFT), based on thermodynamic perturbation theory, explicitly accounts for molecular association, hence, providing a more suitable prediction of thermophysical properties (Devilliers, 2011). This work investigates the performance of the truncated Perturbed Chain-Polar Statistical Associating Fluid Theory (tPC-PSAFT) model in accurately accounting for the effect of molecular association on compressed liquid density in liquid alkane-alcohol mixtures at elevated pressures. This was achieved by comparing the density predictions calculated by the tPC-PSAFT model to novel experimental density data. Isothermal measurements were conducted utilizing an Anton Paar DMA HP densimeter with a upplier stated uncertainty ranging between 0.1 and 1 kg.m-3. Measurements were conducted in the temperature and pressure ranges of 313.15 to 353.15 K and 0.1 to 20 MPa, respectively, over the entire composition range. Furthermore, a test system consisting of ethanol (1) + n-heptane (2) was used to confirm the reliability of the experimental setup and procedure. The density data obtained for the test system was compared to literature and demonstrate excellent correlation of the data, with a maximum relative difference of 0.0005, confirming the reliability of the procedure utilized in this study. The density data of six novel binary systems namely, butan-1-ol/butan-2-ol/2-methylpropan-1-ol (1) + n-octane/n-decane (2) are presented in this work. The maximum expanded combined uncertainties for pressure, temperature, composition and density were 0.032 MPa, 0.02 K, 0.0002 mole fraction, and between 1.10 to 1.12 kg.m-3, respectively. Density data obtained experimentally for all six binary systems comply with the general trend regarding temperature and pressure in that the density of the liquid mixtures decreased with an increase in temperature and increase with an increase in pressure. Furthermore, derived thermodynamic properties namely, the excess molar volume, thermal expansivity and isothermal compressibility were computed for each of the binary systems. Large positive deviations from ideality were noted for the excess volumes for all systems. This is attributed to the different shapes and sizes of the molecules as well as the attractive mixture interactions when compared to those of the individual pure components. In addition, the thermal expansivity and isothermal compressibility demonstrate highly non-linear behaviour which is indicative of systems comprising complex mixtures. The experimental data were compared to correlations/predictions resulting from five models namely, the Modified Toscani-Szwarc (MTS) equation of state (EoS), the Benedict-Webb-Rubin-Starling (BWRS) EoS, Peng-Robinson (PR) EoS, Perturbed Chain-Statistical Associating Fluid Theory (PC-SAFT) model and the truncated Perturbed Chain-Polar Statistical Associating Fluid Theory (tPC-PSAFT) model. Both the MTS and BWRS EoS demonstrated excellent correlation of the data for all six of the binary systems attributed to the empirical nature of the model and the significant number of fitting parameters employed. The maximum root mean square deviation (RMSD) was found in the butan-2-ol (1) + n-octane (2) binary system at RMSD = 4.72 x 10-4. In addition, improvements in model performance were noted for the BWRS EoS at higher temperatures and pressures. The PR EoS demonstrated poor correlation of the density data of the mixtures (exceeding RMSD = 0.024), attributed to the poor prediction of the pure component data by the model and the use of a single binary interaction fitting parameter in the cases of the mixtures. Density predictions from the PC-SAFT model demonstrated significant deviation from experimental data (exceeding RMSD = 0.011) in that the PC-SAFT model underpredicts densities for the binary systems. Furthermore, a progressive deterioration in the model’s performance was noted as the respective alcohol concentration increases. Accurate prediction of the density was however noted for the 2-methylpropan-1-ol binary systems in the alcohol dilute region. In addition, some improvement in model performance was observed at higher pressures and temperatures for the butan-2-ol and 2-methylpropan-1-ol binary systems. The tPC-PSAFT model demonstrated improvement in accurately predicting the density data, for all six systems, when compared to those obtained via the PC-SAFT model, with an improvement in excess of 72% in some cases. In addition, the model performs well in the alcohol dilute region and at high pressures and temperatures. However, a progressive deterioration in the model’s performance is noted as the concentration of the alcohol in solution is increased. This was unexpected as both the PC-SAFT and tPC-PSAFT models explicitly account for molecular association and were theorized to perform well in predicting the alcohol mixture behaviour. The model’s poor performance can be attributed to the lack of high precision pure component parameters currently available in the literature that do not effectively characterize the density of the systems under high pressure. All five models exhibit similar trends to that of the experimental data despite their individual merits and shortcomings.
The application of water pinch analysis at AECI bioproducts.
(2002) Schneider, Janos Pal Zsigmond.; Buckley, Christopher Andrew.; Brouckaert, Christopher John.
AECI Bioproducts (Bioproducts) is part of an industrial complex located at Umbogintwini, approximately 26 km south of Durban, Kwazulu-Natal. This system was selected for water pinch investigation, as it is one of the major users of freshwater on the complex and hence discharges a related quantity of wastewater, amounting to approximately 400 ML per annum. Bioproducts is a manufacturer of l-lysine, which is an animal feed additive. Water stream flowrate and purity data, as well as operating cost information, were obtained from plant records at AECI Bioproducts. Limiting flowrate and purity conditions for the water-using operations were established from a mass balance over the entire system using the Linnhoff-March software, WaterTracker. Subject to the specified constraints and operating costs, the problem was to determine the design of the water-using subsystem. No treatment plants were included in the study, as none exist at the facility. Three scenarios were investigated, which examined the operating variability of one of the evaporators on the site (the AS evaporator), which produces a condensate source of variable purity. The operating cost target and network design for each scenario was determined using the Linnhoff-March software, WaterPinch. Alterations from current operating practice were identified and associated savings (water-using network operating cost and freshwater flowrate) were highlighted. A robust optimal design was identified, with a recycle, which was consistent for all scenarios investigated. The degree of reuse of the AS evaporator condensate source was determined to be dependent on the purity of the source. The limiting constraint was identified at the sea pipeline, for suspended solids (SS): a prohibitively low discharge concentration constraint was identified as posing the major obstacle for saving. The potential for saving was investigated by incrementing the SS concentration constraint and subsequently the free and saline ammonia (FSA) constraint and allowing for the broth effluent to be discharged via the sea pipeline (which was previously disallowed by an effluent exemption). Although relatively small savings were identified through process integration (from 0.61% to 1.56% of the water-using network operating cost), the analysis identified a potential saving of over 70% of the water-using network operating cost, with relaxation of the sea pipeline SS and FSA constraint.
Application of water pinch to an integrated pulp and paper Kraft mill with an already highly closed water system.
(2009) Slabbert, Eric.
Sappi's Ngodwana integrated Kraft pulp and paper mill was used as case study for the application and evaluation of the water pinch technique. The technique of water pinch originates from energy pinch, but uses mass flow and contaminant concentration to identify water and effluent reduction opportunities. The classical meaning of pinch, as defmed by energy pinch has however been changed to a more modem meaning. Historically the terms water or energy pinch was used to refer to the points where two composite curves touched on energy or water graphs. This graphical meaning of pinch is gradually being replaced to refer to the optimal po int proposed by a numerical solver beyond which improvement of the water network is no longer possible for the given inputs. The water pinch technique was applied by means of a numerical solver that used mixed integer non-linear programming to optimise to the minimum cost for running the water network under investigation. The problem defmition was defined in terms of costs associated with the use of utilities, raw material, treatment facilities and process units. It was also possible to define factors such as environmental impact, corrosion, fouling, scaling, cooling tower treatment cost, legal risk etc in terms of a penalty cost. The water pinch technique has been refined in software packages that are user friendly, ca~ble of handling multi-contaminants and suitable for varying flows. The software package WaterPinch by Linnhoff March was used. The case study was applied on Ngodwana mill that has an already highly closed water system with effluent generation rates as low 20 kL per ton of pulp and paper. The pinch study included sodium, chloride, calcium, suspended solids and COD as contaminants. The study investigated different applications of the pinch technique. The following was concluded: • The mill's understanding of its current restrictions, ()l pinch points, of its water network was confirmed. No new pinch points have been identified of which the mill was not aware. This indicates that the mill was already highly knowledgeable about its water system. This was expected of a mill that has a very low specific-effluent-generation rate. Water pinch was unable to significantly improve on the effluent generation rate of the mill. • The pinch analysis has identified opportunities of mixing small quantities of waste streams into process water streams to replace fresh water. These changes can introduce minor water savings and new risks to the process that have to be understood better before implementation. • The mill has progressed far with the design and costing of a proposed effluent treatment plant (ERPl). The integration of this treatment plant into the water network was investigated using the pinch technique. The pinch solver suggested a totally different approach to the integration of the ERPI plant compared to design of the mill. The mill's design revolves around the treatment of low chloride streams in the ERPl plant and using of the treated water as make-up to the cooling towers. Sodium was recovered as raw material from the cooling towers' blow-down. Pinch proposed treatment of the high cWoride containing streams and returning the streams to users suitable of using high chloride water. The network proposed by mill's design generates 8.2 MLlday effluent less than the pinch proposal, and recovers sodium as raw material. The proposal presented by pinch is not recommended and points to the difficulty in simulating factors, such as raw material recovery, in a pinch analysis. • Users for the excess storm water were identified using water pinch and will be suitable for implementation. The mill has mwever decided on alternative sinks for the storm water based on considerations such as process inter-dependency, risks associated with contamination and general management philosophy for the different systems in the mill. These considerations could have been included into the pinch solver, but were not because it was of interest what the second best option would be. • The pinch investigation proved useful to confirm certain understandings of the mill. The investigation confirmed the difficulty of improving the water systems of the mill due to the fact that Ngodwana is already a highly closed and integrated mill. Numerous smaller process changes have been identified by the pinch solver and could be investigated further for smaller process improvements. • It i; recommended that pinch technology be applied again when the mill plans to make major process changes or expansions. It is also recommended to use water pinch on a more frequent basis in smaller sections of the mill or for other evaluations in the mill. As a group Sappi could benefit from the use of water pinch, especially in situations where the water network of the mill is not already water efficient. • The recommendations and conclusions in this report have not been subjected to technical and economical feasibility studies. Extensive further studies must be conducted before implementation of any of the results. Further studies must include impacts from process dynamics, long term effects, impacts from other contaminants that have not been simulated, etc.
Assessing the treatability of textile effluents in an activated sludge system.
(2014) Mashava, Arnold.; Buckley, Christopher Andrew.; Brouckaert, Christopher John.
Assessing the treatability of a textile effluent through the activated sludge process required the development of analytical protocols and evaluating their suitability in providing receiving municipal wastewater treatment plants with systematic methodologies for predicting: (i) soluble dye effluent decolourisation through the activated sludge process (ii) impact of surfactants on oxygen transfer in the activated sludge system (iii) subsequent biodegradability of these surfactant effluents. Decolourisation was assessed through spectrophotometric computations of the mass of dye remaining in the activated sludge supernatant. Oxygen transfer was quantified from estimates of volumetric oxygen transfer coefficients which were computed from the modified form of the Lewis-Whitman interfacial mass transfer model which took into account the oxygen uptake rate from the respiring microbial species Biodegradability of the surfactant effluent was computed from the mass of soluble biodegradable substrates assimilated by the active sludge system during exogenous respiration The mass of the dye particles removed from solution attained an asymptotic value after 1 h and this implied adsorption equilibrium. A comparison between the adsorption equilibrium attained after 1 h and the municipal activated sludge system hydraulic residence time of 6 h led to the conclusion that soluble colour removal in receiving municipal activated sludge systems is not rate limited and it was therefore not necessary to accurately predict the adsorption kinetics. Instead, the adsorptive capacity of the activated sludge and extent of dye effluent decolourisation is of greater significance. Instantaneously after dosing the activated sludge system with the surfactant effluent, computed estimates of the volumetric oxygen transfer coefficient exhibited sudden and pronounced increments which simultaneously coincided with pronounced increments in the non-linear regression confidence level error bounds associated with each mass transfer coefficient computation. It was theorised that the surfactant effluent imparted some form of interference to the Clark dissolved oxygen sensor’s dissolved oxygen measurement mechanism and this resulted in erratic data points that did not fit onto the model. Comparative computations of volumetric oxygen transfer coefficients in the presence of a non-surfactant substrate such as CH3COOH should be conducted for purposes of elucidating increments in the mass transfer coefficients as a result of reaction-enhanced mass transfer from increments resulting from the impact of the surfactant effluent on either the liquid film mass transfer coefficient or the interfacial area or both. Further refinements are required in automating the methodology for computing volumetric oxygen transfer coefficients and generating scatter plots of the mass transfer coefficients as a function of time from automated real-time feeds of dissolved oxygen time series data logged by dissolved oxygen online instrumentation. Biodegradability numerical estimates were all far less than the estimates reported in literature by surfactant manufacturers and it was postulated that the erratic dissolved oxygen time series data points resulting from the dosing of the surfactant effluent were also extended to the biodegradability computations. It is also highly probable that the pronounced dissimilarities in biodegradability estimates were a result of either the presence of toxic components in the surfactant effluent which resulted in the gradual inhibition of microbial activity or a significant presence of slowly biodegradable and inert soluble substrates in the surfactant effluent which were not depleted through aerobic utilisation by heterotrophic microbial populations.
Assessment and feasibility of converting municipal solid waste to biogas: a South African case study.
(2021) Gaogane, Gaogane Jephtah.; Sithole, Bishop Bruce.; Trois, Cristina.
The present energy crisis in South Africa warrants the need for an alternative and sustainable energy supply. As a sustainable clean energy carrier, biogas has been demonstrated to be a promising renewable energy source for the generation of heat and electricity. The organic fraction of Municipal Solid Waste (MSW) has been reported as a promising feedstock for biogas production and characterisation of MSW is the basis towards successful waste to energy programs. The use of inappropriate equipment and technology choices based on insufficient data on waste volumes and composition have resulted in the failure of many interventions previously introduced in South African municipalities. Assessing the composition and quantity of available biomass for anaerobic digestion (AD), suitable pre-treatment technologies to enhance biogas production as well as optimization of AD parameters such as pH, temperature and substrate ratio were the core components of this research project. The digestate was evaluated and potential use as fertilizer and feedstock for pyrolysis assessed. A mesophilic bench-scale AD of Cow Dung (CD) and Fruit and Vegetable waste (F&V) obtained from a F&V market was conducted. F&V forms the greatest waste in the country, and this facility generates on average 2560 tonnes of waste per annum. This study concludes that utilisation of MSW for AD relies heavily on characterisation data, which is only possible through separation at source. The study recommends the development of a municipal organic waste facility and equally important, diversion of high-end food chains from entering the landfills. Other technologies such as Mechanical Biological Treatment (MBT) can be revisited for possible waste to energy programs at landfill leading to landfill space savings and reduced pollution. Waste pickers at landfills can be employed for this purpose as separation specialists. Bench-scale AD revealed that the benefits of substrate pre-treatment outweighed the effects of co-digestion ratio and pH. Reducing particle size from 1-2mm to <1mm, doubled the methane gas generation in a much shorter time and removed pH induced microbial inhibition in unbuffered reactors. Optimal pH was observed at 7.5-8.5. A co-digestion ratio of 80:20 (CD:F&V) produced higher methane yield for all pH variations in comparison to 60:20. The Digestate measured an average volatile solids loss of 46.4% with a C:N ratio of 12 and a heating value (HV) of 4.30 MJ/kg. Metal analysis of digestate showed presence of Nb, Sr, Si, N, P and K as constituents returned to the soil. The investigation of the digestate as a potential feedstock for pyrolysis yielded a carbon rich biochar with an HV value of 11.5 MJ/kg at 500 oC and a bio-oil rich in phenols, ketones and carboxylic acids which are important industry products.

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