Chemical Engineering

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A framework for modelling the interactions between biochemical reactions and inorganic ionic reactions in aqueous systems.
(2022) Brouckaert, Christopher John.; Lokhat, David.
Bio‐processes interact with the aqueous environment in which they take place. Integrated bio‐process and three‐phase (aqueous–gas–solid) multiple strong and weak acid/base system models are being developed for a range of wastewater treatment applications, including anaerobic digestion, biological sulphate reduction, autotrophic denitrification, biological desulphurization and plant‐wide wastewater treatment systems. In order to model, measure and control such integrated systems, a thorough understanding of the interaction between the bio‐processes and aqueous‐phase multiple strong and weak acid/bases is required. This thesis is based on a series of five papers that were published in Water SA during 2021 and 2022. Chapter 2 (Part 1 of the series) sets out a conceptual framework and a methodology for deriving bioprocess stoichiometric equations. It also introduces the relationship between alkalinity changes in bioprocesses and the underlying reaction stoichiometry, which is a key theme of the series. Chapter 3 (part 2 of the series) presents the stoichiometric equations of the major biological processes and shows how their structure can be analysed to provide insight into how bioprocesses interact with the aqueous environment. Such insight is essential for confident, effective and reliable use of model development protocols and algorithms. Where aqueous ionic chemistry is combined with biological chemistry in a bioprocess model, it is advantageous to deal with the very fast ionic reactions in an equilibrium sub‐model. Chapter 4 (part 5 of the series) presents details of how of such an equilibrium speciation sub‐model can be implemented, based on well‐known open‐source aqueous chemistry models. Specific characteristics of the speciation calculations which can be exploited to reduce the computational burden are highlighted. The approach is illustrated using the ionic equilibrium sub‐model of a plant‐wide wastewater treatment model as an example. Provided that the correct measurements are made that can quantify the material content of the bioprocess products (outputs), the material content of the bioprocess reactants (inputs) can be determined from the bioprocess products via stoichiometry. The links between the modelling and measurement frameworks, which use summary measures such as chemical oxygen demand (COD) and alkalinity, are described in parts 3 and 4 of the series, which are included as appendices to the thesis. An additional paper, presenting case study on modelling an auto‐thermal aerobic bio‐reactor, is included as a third appendix, as it demonstrates the application of some of the principles developed in the series of papers.
Activity of complex multifunctional organic compounds in common solvents.
(2009) Moller, Bruce.; Ramjugernath, Deresh.; Rarey, Jurgen.
The models used in the prediction of activity coefficients are important tools for designing major unit operations (distillation columns, liquid-liquid extractors etc). In the petrochemical and chemical industry, well established methods such as UNIFAC and ASOG are routinely employed for the prediction of the activity coefficient. These methods are, however, reliant on binary group interaction parameters which need to be fitted to reliable experimental data. It is for this reason that these methods are often not applicable to systems which involve complex molecules. In these systems, typically solid-liquid equilibria are of interest where the solid is some pharmaceutical product or intermediate or a molecule of similar complexity (the term complex here refers to situations where molecules contain several functional groups which are either polar, hydrogen bonding, or lead to mesomeric structures in equilibrium). In many applications, due to economic and environmental considerations, a list of no more than 20 solvents is usually considered. It is for this reason that the objective of this work is to develop a method for predicting the activity coefficient of complex multifunctional compounds in some common solvents. The segment activity coefficient approaches proposed by Hansen, MOSCED and the NRTL-SAC models show that it should be possible to “interpolate” between solvents if suitable reference solvents are available (e.g. non-polar, polar and hydrogen bonding). Therefore it is useful to classify the different solvents into suitable categories inside which analogous behaviour should be observed. To accomplish this, a significant amount of data needs to be collected for the common solvents. Data with water as a solvent was freely available and multiple sources were found with suitable data. Both infinite dilution activity coefficient (y∞) and SLE (Solid-Liquid Equilibrium) data were used for model development. The y∞ data were taken from the DDB (Dortmund Data Bank) and SLE data were taken from Beilstein, Chemspider and DDB. The limiting factor for the usage of SLE data was the availability of fusion data (heat of fusion and melting temperature) for the solute. Since y∞ in water is essentially a pure component property it was modelled as such, using the experience gained previously by this group. The overall RMD percentage (in ln y∞) for the training set was 7.3 % for 630 compounds. For the test set the RMD (in ln y∞) was 9.1 % for 25 fairly complex compounds. Typically the temperature dependence of y∞ data is ignored when considering model development such as this. Nevertheless, the temperature dependence was investigated and it was found that a very simple general correlation showed moderate accuracy when predicting the temperature dependence of compounds with low solubility. Data for solvents other than water were very scarce, with insufficient data to develop a model with reasonable accuracy. A novel method is proposed for the alkane solvents, which allows the values in any alkane solvent to be converted to a value in the solvent hexane. The method relies on a first principles application of the solution of groups concept. Quite unexpectedly throughout the course of developing the method, several shortfalls were uncovered in the combinatorial expressions used by UNIFAC and mod. UNIFAC. These shortfalls were empirically accounted for and a new expression for infinite dilution activity coefficient is proposed. This expression is however not readily applicable to mixtures and therefore requires some further attention. The method allows for the extension of the data available in hexane (chosen since it is a common solvent for complex compounds). In the same way as the y∞ data in water, the y∞ data in hexane were modelled as a pure component property. The overall RMD percentage (in ln y∞) for the training set was 21.4 % for 181 compounds. For the test set the RMD (in ln y∞) was 11.7 % for 14 fairly complex compounds. The great advantage of both these methods is that, since they are treated as pure component properties, the number of model parameters grows linearly with the number of groups, unlike with mixture models (UNIFAC, ASOG, etc.) where it grows quadratically. For both the water and the hexane method the predictions of the method developed in this work were compared to the predictions of UNIFAC, mod. UNIFAC, COSMO-RS(OL) and COSMO-SAC. Since water and hexane are not the only solvents of practical interest, a method was developed to interpolate the alcohol behaviour based on the water and hexane behaviour. The ability to predict the infinite dilution activity coefficient in various solvents allowed for the prediction of various other properties, viz. air-water partition coefficient, octanol-water partition coefficient, and water-alcohol cosolvent mixtures. In most cases the predictions of these properties were good, even for the fairly complex compounds tested.
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 a pilot-scale anaerobic baffled reactor treating domestic wastewater.
(2009) Foxon, Katherine Maria.; Buckley, Christopher Andrew.
This thesis presents a chemical, microbiological and mathematical analysis of an anaerobic baffled reactor (ABR) treating domestic wastewater. The purpose of this study was to gain an understanding of the mechanisms of treatment of domestic wastewater in an ABR at pilot-scale, and to use this understanding to develop some guidelines for the design of ABR technology for the anaerobic treatment or pre-treatment of domestic wastewater. Previous research has been undertaken on ABR technology, but no detailed studies of the performance of an ABR on domestic wastewater at pilot-scale have been reported. In this thesis, operating data from a 3 000 ℓ pilot-scale ABR are presented and analysed. Two hypotheses were proposed: that (i) the baffled design of the reactor would facilitate phase separation whereby acidogenic and methanogenic processes predominate in different physical locations in the reactor; and (ii) the critical design parameter is the applied hydraulic retention time. The principle findings of this research were: • The pilot-scale ABR functioned as a solids retention device. Particulate material was retained through settling in the first compartment, forming a gel-like matrix. Reduction of solids occurred through anaerobic conversion to CH4 and CO2. • Partial phase separation of acidogenic and methanogenic communities was observed. • The major factor that controlled biomass washout rate and therefore reactor performance was upflow velocity in each compartment. At higher upflow velocities, slow growing microorganisms failed to establish, resulting in increased solids accumulation rates, while at lower upflow velocities, stable digestion proceeded. • Relatively poor treatment rates were obtained due to the low inherent alkalinity of waters in eThekwini municipality resulting in low operating pH values. • Insufficient pathogen reduction was observed indicating that post-treatment of effluent would be required. It was concluded that the benefit of the baffled design was related to the system’s solids retention characteristics and that the critical design parameters for an ABR domestic wastewater treatment unit were compartment upflow velocity and applied hydraulic retention time.
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 non-Newtonian behavior of crude oil: experimental study annumerical modeling using computational fluid dynamics (CFD) technique.
(2020) Mohammadi, Amirabbas.; Mkhize, Ntandoyenkosi Malusi.
Abstract available in the PDF.
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 gas hydrates in cold storage technology : experimental study and thermodynamic modeling.
(2015) Hashemi, Hamed.; Ramjugernath, Deresh.
The ever-increasing demands for air conditioning technology especially in residential areas results in a severe imbalance between power generating utilities, especially during peak usage hours. To provide the required peak capacity, expensive peak-generators are compulsory. Hence, researchers are compelled to find an effective air conditioning system which can be utilized during peak-hours with the minimum of electrical consumption. One solution to this problem is to shift the electrical consumption from peak-hours to off-peak hours by a combination of a cold storage technology with the air conditioning system. In the cold storage system, the cold energy can be stored by a medium during off-peak hours (e.g. ice or water) and it can be released for use at peak hours. An air conditioning system which operates with cold storage technology usually consists of a storage medium, a storage tank, a coolant circulator, a pump and a condenser. Due to the fundamental role of storage medium in cold storage systems, various investigations have been performed in order to design an applicable storage tank. Ice, eutectic salt, and water are the most common materials being used as storage materials in cold storage applications. However, the application of these conventional materials as storage medium is not practical, due to their formation at low temperatures, their low enthalpy of dissociation and their low density of cold storage. It was found that most refrigerant hydrates can be utilized as a suitable cold storage medium in air conditioning systems due to their significant properties such as high enthalpy of formation/dissociation close to that of ice, and temperatures of formation above the freezing point of water. In this study an extended review on the application of clathrate/semiclathrate hydrates in cold storage systems is performed. The gas hydrate dissociation conditions of refrigerants R23, R134a, R125a, R22, R116, R410A, R407C, R408A, R508B, R404A, R406A, R427A and R507C have been measured experimentally using an isochoric pressure search method. From the measured experimental dissociation data, the enthalpies of hydrate dissociation are evaluated. Results indicate that R507C has the highest enthalpy of dissociation amongst the other refrigerant blends. R134a, R410A, R407C and R427A with low pressure of hydrate formation/dissociation, show the most suitable behaviour to be used in cold storage applications. A thermodynamic model with the ability to correlate dissociation conditions of refrigerant hydrates in the different phase equilibrium boundaries (Hydrate-Ice-Vapour, Hydrate-Aqueous solution-Vapour, Hydrate- Hydrate-Aqueous solution-Liquid refrigerant) has been proposed. The difference between model predictions and experimental data is reasonable. Furthermore, in order to examine the rate of the refrigerant hydrate formation, an experimental study has been performed on the kinetics of the hydrate formation of the refrigerant blends namely R407C, R410A, R507C, R404A, R406A, R408A and R427A. The induction time of hydrate formation, apparent rate constant of the hydrate reaction, water to hydrate conversion during hydrate nucleation and growth, storage capacity and the rate of hydrate formation of above mentioned refrigerants at different initial conditions (pressures and temperatures) have been calculated using a kinetic model. The results demonstrate that in the presence of pure water R407C has the maximum apparent rate constant, appropriate induction time, and highest storage capacity at temperate pressures and temperatures amongst the eight refrigerants studied. The effect of sodium dodecyl sulfate (SDS) with different concentrations of 400, 500 and 600 ppm on hydrate nucleation and growth rate was investigated. In contrast to the refrigerants R406A, R404A, R408A and R427A an inhibition effect of SDS on gas hydrate nucleation rate was found for the refrigerants R407C, R410A and R507C. The most relevant kinetic results were found for the system R406A + 400 ppm SDS solution.
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.

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