Doctoral Degrees (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.
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 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.
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.
Applications of fluorocarbons for supercritical extraction in the petroleum industry.
(2016) Williams-Wynn, Mark Duncan.; Ramjugernath, Deresh.; Naidoo, P.
The majority of supercritical processes utilise carbon dioxide (CO2) as the principal solvent, because CO2 has many attributes that make it an ideal supercritical fluid (SCF) solvent. This study investigates the possibility of replacing CO2 with trifluoromethane or hexafluoroethane, because of the poor performance of CO2 in cases where more polar and heavier molecular weight solutes must be extracted. Several applications in the petroleum industry, such as oil sludge treatment and the treatment of contaminated soils, are discussed. Due to the large number hydrocarbons present in such applications, a selection of solutes that could be used to simulate a simplified stream were chosen for these investigations. These selected solutes were n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane, 1-hexene, 3-methylpentane, methylcyclohexane, toluene and water. High-pressure vapour-liquid equilibria and vapour-liquidliquid equilibria for binary systems containing either trifluoromethane or hexafluoroethane, with these solutes were measured using a static-analytic apparatus at temperatures of between (272.9 and 313.2) K. For several systems, the phase equilibria data were verified using bubble-point pressures measured with a static-synthetic, variable-volume cell. Parameters for thermodynamic models were obtained by regression of the experimental data for the binary systems. The models provide a good representation of the majority of the systems investigated, and were therefore also used to estimate portions of the critical locus curves. These critical locus curves were compared to the critical loci that were extrapolated from the sub-critical coexistence data as well as critical loci that were measured with a critical point determination apparatus. There is satisfactory agreement between the calculated, the extrapolated and the measured critical loci. The thermodynamic models were used to simulate the separation of several hydrocarbon-water emulsions using either CO2, trifluoromethane, hexafluoroethane or mixtures thereof. The simulations confirmed that trifluoromethane, hexafluoroethane as well as mixtures thereof, provide improved performances (recoveries and yields) when used as alternative solvents in the SCF extraction of these systems. An economic analysis of a SCF extraction process was performed to investigate the performance of the solvents, and if such SCF extraction processes, using a mixture of trifluoromethane and hexafluoroethane, would provide an economically competitive treatment process for hydrocarbon-water emulsions.
Beneficiation of chicken feathers and sawdust waste biomass: extraction of keratin and cellulose nanocrystals for use as binders in particleboard production.
(2020) Fagbemi, Olajumoke Deborah.; Sithole, Bishop Bruce.
The wood industry consumes large quantities of synthesis adhesives accounting for more than 65% by volume of the adhesives used worldwide. Synthetic adhesives are formaldehyde-based and that cause environmental pollution and affect human health. Hence, there is a growing interest in bio-adhesives sourced from natural sources: plant and animal, these could be a suitable replacement for environmental toxic formaldehyde-based binders. In addressing the problems mentioned above, from both economic and environmental points of view, this study focused on the beneficiation of waste chicken feathers generated by poultry slaughterhouses and waste sawdust from the sawmilling industry into binders to replace fossil-based binders and explore their use in the production of wood panel particleboards. The linear and interactive effect of process condition on the extraction efficiency of keratin protein were modelled and optimized. To the best of the author’s understanding, the work presented here is first for South Africa as a country. Extraction processes with varying key process parameters were experimentally assessed for protein and keratin yield. The novel extraction procedure used a hybrid of two reducing agents; sodium hydroxide and sodium bisulphite, under mild concentrations to minimize the keratin protein structure's degradation. The extraction variables, optimised using Response Surface Methodology, were temperature (87°C), extraction time (111 minutes), sodium hydroxide (1.78%), and sodium bisulphite (0.5%). Analysis of the protein hydrolysate content showed the elemental composition of 13.85% N, 47.25% C, 6.90% H and 2.8% S, and a molecular weight range between 15 and 3 kDa; ideal characteristics for bio-binder applications. Keratin and cellulose nanocrystals were each evaluated separately as bio-adhesives for particleboard production. The efficiency of the formulated bio-adhesives and the mechanical strength performances of their fabricated particleboards were also assessed. Results showed that keratin on its own did not display significant binding properties; however, these were significantly improved by adding the citric acid-based polyamide-epichlorohydrin cross-linking agent. The fabricated particleboard's mechanical strength performance met the 1-L-1 grade specification of the American National Standards Institute. Moreover, the beneficiation of extracted keratin protein hydrolysate from waste chicken feather with incorporated cellulose nanocrystals for bio-adhesive formulation and particleboard fabrication was investigated. The FTIR spectra confirmed the covalent bonding between the azetidinium of the citric acid-based polyamide-epichlorohydrin cross-linking and the hydroxyl groups of the keratin protein hydrolysate. The mechanical strength performance of the fabricated particleboard met the specification for the 1-L-1 grade of the American National Standards Institute (A208.1). 6, 5 and 1184, 34 MPa, were the respective values obtained for modulus of rupture and modulus of elasticity of the panels made with keratin-based adhesive. Additionally, the keratin-based adhesive incorporated with cellulose nanocrystals as a filler enhanced the static bending and bonding strength properties of the formulated bio-adhesive. Furthermore, the valorisation of wood sawdust into cellulose nanocrystals (CNC) for application as a binder in the manufacture of particleboard was also carried out. The cellulose nanocrystal extracted from wood sawdust using acid hydrolysis and an oxidizing agent, incorporated with crosslinking agents, viz., CNC-glyoxal, CNC-hexamine, CNC-polyamide-epichlorohydrin, and CNC-polyethylene to make cross-linked bio-binders. X-ray diffraction (XRD) indicated high crystallinity index (78%) of the CNC and typical nano dimensions of 2.1–10 nm for diameter and 150-350 nm for length as revealed by the transmission electron microscope (TEM). Thermogravimetric analysis (TGA) and differential thermogravimetric (DTG) showed high thermal stability (250 – 400 ℃) of the CNC. Significant mechanical strength performances of the particleboard panels were evident in the modulus of rupture (MOR) and the modulus of elasticity (MOE) of the CNC-binder fabricated particleboard. The panels met grade 1-L-1 specification of the American National Standards Institute A208.1. Similarly, the incorporation of cross-linking agents enhanced the static bending and bonding strength properties of the formulated CNC-binders. Hence, the research conducted in this thesis demonstrated the potential of bio-binders produced from waste biomass, viz., chicken feathers and sawdust to replace fossil-based binder.
Beneficiation of kraft pulp millwaste: using green liquor dregs in treatment of acid mine drainage as a new disposal solution in South Africa.
(2020) Sebogodi, Keolebogile Revelation.; Sithole, Bishop Bruce.; Johakimu, Jonas Kalebe.
Globally, water scarcity, depletion of non-renewable natural resources, handling and management of industrial wastes are not only significant environmental and economic burdens but also impact human and environmental health. In South Africa, the mining industry is essential to the country and a significant contributor to the GDP of the country. Two major ones are gold and coal mining. Unfortunately, the industries generate large amounts of acid mine drainage (AMD) that originate from the mining activities. The AMD is formed when the 3% pyrite mineral found in the mine effluent dams and voids of gold and coal mines is oxidised upon exposure to water and oxygen resulting in the formation of sulphuric acid which dissolves and leaches surrounding rock and soil matter thus introducing toxic metals into the aquatic waters and biota thus negatively impacting human, animal, and environmental health. Currently, this acidic discharge is neutralised by the use of alkaline reagents such as CaO, Ca(OH)2, NaOH, and CaCO3. However, these chemicals are expensive or are not sustainably resourced in the case of the widely used calcium carbonate. Possible landfilled, industrial, carbonic wastes such as the green liquor dregs (GLDs), from Kraft pulp mills, could be used as sustainable alternatives for the CaCO3 and its derivatives in pre-treating AMD. These wastes streams are produced at the rate of 7-15 kg/ton of dry pulp. In South Africa, this translates to ~100 000 tons of GLDs that are produced and landfilled annually. However, this is an environmentally challenging and not cost-effective practice. Thus, this study entailed characterising GLDs produced in South Africa, evaluating them for the potential of neutralisation of AMD, and optimising the neutralisation process variables. This is the first time that this type of study has been conducted in South Africa. Furthermore, the neutralisation of the coalfields AMD with GLDs has not yet reported in the literature and this is the first time the optimisation of AMD treatment by GLDs is being studied. The study entailed statistically designed experiments that employed a Box-Behnken Design and Response Surface Methodology to optimise the variables involved in the neutralisation process. The results indicate that although characteristics of GLDs from different mills differ they all are effective in neutralisation of AMD from gold or coal mines and their neutralisation potential is similar to that of calcium carbonate. Nevertheless, the SEM/EDX, ICP-AES/ICP-MS, XRF, and XRD analysis on the sludge that emanated from either of the neutralisation processes showed that the neutralisation of AMD using GLDs is effective and enables precipitation, co-precipitation, or adsorption of the different metals from the AMD. The pH of AMD could be raised to optimum pH process value and reduce the acidity at a low dosage, thus offering a competitive advantage over commercial CaCO3. Thus, using GLDs for neutralisation of AMD can be an effective symbiotic process that can benefit two industries in managing their waste discharges: the Kraft pulp industry and the mining industries. The results obtained from the optimisation of the variables (neutralising reagent dosage, process time, and stirring speed) involved in the neutralisation process showed that the reagent dosage was the most significant variable while the stirring speed was the least significant one. The models for all the GLDs and reference materials were proven to be significant because all of them had a p-value of <0, 000001 and their R2 and Adjusted R2 were close to 1.
Bioethanol production from excess food crops in Nigeria: process design, optimization, and techno-economic analysis.
(2021) Awoyale, Adeolu Abiodun.; Lokhat, David.
The global drive for diversification of energy sources, particularly by focusing less on non-renewable fossil fuels and harnessing renewable energy resources like bioethanol, has motivated this research work. Before the last 10 years, bioethanol meant for use as fuel was produced from carbohydrate-rich crops such as cassava, yam, maize, millet, rice amongst others. Because the production of bioethanol from these food crops has been envisaged to jeopardize food security, the focus has been shifted to the production of bioethanol from the residues left behind after processing the food crops. These residues can be classified as lignocellulosic biomass. The major concentration of this study is the production of bioethanol from residues of food crops, namely, corn cobs, rice husks, sugarcane bagasse, cassava peels, and yam peels. The biomass used in this research were sourced from different locations in Nigeria, where they are found in abundance at certain seasons yearly. In the course of the work, the biomass were sieved into two mesh sizes of 300 and 425 microns, and also some of the biomass as well as all the five biomass were all mixed and firstly characterized to evaluate the effects of particle size as well as hybridized biomass mixtures on the end products and production efficiency of bioethanol. The effects of the adopted pretreatments in this study on the biomass were also investigated, as such, three types of pretreatments were adopted in this study namely; combined hydrothermal and acid pretreatment, combined hydrothermal and alkaline pre-treatment, and hydrothermal only pretreatment. The results of the characterization of the different biomass, including the hybridized biomass after pretreatment showed the pore features for hybridized corn cobs and rice husks biomass have the maximum specific surface area and pore volume of 1837 m2/g and 0.5570 cc/g respectively. Also, the values of the cellulose content improved slightly with the pretreatment and the value of the lignin content decreased considerably. The cellulose values range from 34.2 to 36.5 wt% for the acid, alkali and hot water pretreated hybridized biomass. Releases from the pretreatment process to air, soil, and water were measured with SimaPro. The environmental impact categories accessed include global warming potential (GWP)/climate change, and acidification (AP). With a mean value of 15.82 kg CO2 (eq), the alkaline pretreatment using sodium hydroxide shows the highest release of GHG emissions, while acid pretreatment employing dilute sulphuric acid generated a mean value of 8.68 kg CO2. Hybridized feedstocks of cassava peels plus yam peels, and corn cobs plus rice husks biomass, were optimized using the Response Surface Methodology (RSM) centred on the statistical design of experiments (DOE) of the Box-Behnken design (BBD), in the production of bioethanol. The BBD was harnessed using a 3-level, 3-factor process variables using pH, time, and particle size. The bioethanol yield from the two hybridized biomass feedstocks was predicted by the developed quadratic polynomial models from BBD. The hybridized rice husks plus corn cobs biomass with a maximum bioethanol yield of 160 ml/1500 g biomass gave a better prospect for bioethanol production when compared with hybridized cassava peels plus yam peels biomass with a maximum bioethanol yield of 125 ml/1500 g biomass. This reinforces the finding that hybridizing the feedstocks enhances the capacity for better bioethanol yield after fermentation. The economic analysis of the produced bioethanol gave a price of 0.41 USD/l, which is a good deal as it compares favorably well with the 0.45 USD/l price of ethanol in the Nigerian open market.
Carbon dioxide encapsulation in methane hydrates.
(2022) Ndlovu, Phakamile.; Naidoo, Paramespri.; Babaee, Saeideh.; Moodley, Kuveneshan.
Coal mining and petroleum refining processes face extreme pressure under climate change and global warming threats. Hence alternative sustainable and renewable energy sources must be made available for the rising energy demands. Natural gas found in permafrost and seabed areas in the form of gas hydrates possess vast amounts of low-carbon methane gas, which can replace fossil-based energy sources. The capture and storage of carbon dioxide gas in natural gas hydrate beds with the release of methane gas is a sustainable route under intense research. This study investigates the methane-carbon dioxide (CH4-CO2) replacement reaction mechanisms and the improvement of the process using different techniques, namely, additives, secondary gas, and thermal stimulation. Firstly, the gas hydrate dissociation measurements for the former gases utilized in the study were performed. This was followed by kinetic measurements with nanoparticles (aluminum oxide, copper oxide, and graphene nanoplatelets) and chemical additives (zinc oxide powder, graphite powder, and magnesium nitrate hexahydrate crystals) in the presence of sodium dodecyl sulfate (SDS) to affect kinetic or thermodynamic improvement in hydrate formation. The kinetic parameters investigated were induction time, hydrate storage capacity, water consumed in hydrate formation, fugacity of the gaseous phase, and the ratio of gas consumed to moles of water. Graphene nanoplatelets were selected for replacement reaction based on promising results obtained from the kinetic studies. The CH4-CO2 replacement process was performed in a 52 cm3 equilibrium cell using deionized water and nanoparticles. Also, a new experimental setup with a 300 cm3 reaction vessel was designed and assembled for CH4-CO2 replacement in the presence of synthetic silica sand. The results from kinetic studies showed an improvement in the hydrate formation kinetics due to the presence of nanoparticles. The CO2 hydrate formation kinetics obtained a maximum storage capacity of 51 (v/v), with 1.2 wt.% graphene nanoplatelets which also produced a maximum water conversion of 25%. When nanoparticles were added, the induction time for CO2 hydrate in deionized water was reduced from 9 minutes to less than one minute. Graphite powder with a concentration of 1.2 wt.% had the highest rate of gas uptake of 0.0024 (mol of gas/ mol of water. min). In CH4 kinetics, the induction time was reduced from 18 minutes with deionized water to less than one minute due to addition of nanoparticles. A maximum storage capacity of 28.5 (v/v), water-to-hydrate conversion of 13.09%, rate of gas uptake of 0.0089 (mol of gas/ mol of water. min), and gas consumption of 0.0238 moles were obtained with 0.1 wt.% CuO + 0.05 wt.% SDS. Also, CH4-CO2 replacement measurements showed that an 80 mol% N2/20 mol% CO2 gas mixture yielded a CH4 replacement efficiency of 17.04% at a temperature of 274.77 K and pressure of 5.34 MPa. The highest amount of CO2 sequestrated was 57.03%, and 28.77% was the highest CH4 replacement efficiency. These results were obtained using pressurized CO2 with application of thermal stimulation at a temperature of 275.90 K and pressure of 5.66 MPa. In the replacement reaction with silica sand, the maximum amount of CH4 replaced was 37.49% with the pressurized CO2 at a pressure of 7.01 MPa and temperature of 276.43 K. Applying thermal stimulation and adding secondary gas (N2) improved CO2 sequestration from 51.73% to 76.63%. These outcomes are vital in applying hydrates in gas storage and CO2 sequestration.
Carbon dioxide removal from coal power plants : a review of current capture techniques and an investigation of carbon dioxide absorption using hybrid solvents.
(2014) Osman, Khalid.; Ramjugernath, Deresh.; Coquelet, Christophe.
The aim of this project was to identify and assess all possible solutions to reduce carbon dioxide (CO2) emissions from coal power plants in South Africa, identify the most likely solution to be implemented industrially in the short to mid-term future, and contribute towards its development through lab measurement and further research. This thesis thus contains a substantial literature review conducted on the current state of CO2 emissions in South Africa, conventional and novel coal power plant processes, modes of CO2 capture, criteria regarding the implementation of CO2 capture techniques, and the various CO2 capture techniques currently investigated with varying levels of development. The study found gas absorption using solvents to be the most likely mid-term CO2 capture technique to reach industrial implementation. However, certain challenges still need to be overcome, particularly due to numerous limitations of current solvents, to make this technique feasible for CO2 capture. In an attempt to overcome the main challenge of solvent absorption capacity, it was decided to investigate the use of ionic liquids for CO2 absorption. An in-depth review of ionic liquids was conducted, as well as a review of measurement techniques and modelling of gas absorption in alkanolamine and ionic liquid solvents. Four ionic liquids, namely methyl trioctyl ammonium bis(trifluoromethylsulfonyl)imide [MOA][Tf2N], 1-butyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide [Bmim][Tf2N], 1-butyl-3-methyl imidazolium tetrafluoroborate [Bmim][BF4], and 1-butyl-3-methyl imidazolium methyl sulphate [Bmim][MeSO4] were tested for CO2 and O2 absorption by measuring equilibrium Pressure-Temperature-Liquid mole fraction (P-T-x) data. Measurements were conducted using an Intelligent Gravimetric Analyser (IGA-01) at 303.15, 313.15, and 323.15 K. CO2 partial pressures of 0.05 to 1.5 MPa and O2 partial pressures of 0.05 to 0.7 MPa were investigated. Furthermore, density and refractive index measurements were conducted for all solvents. The ionic liquids were benchmarked against other ionic liquids and conventional alkanolamine solvents for CO2 absorption capacity and selectivity. The study found that ionic liquids achieved higher CO2 absorption capacity at high pressure than conventional alkanolamine solvents, but very low absorption capacity at low pressure. Of the ionic liquids studied, [Bmim][BF4] and [Bmim][Tf2N] achieved high CO2 absorption and high CO2 selectivity over O2. Therefore, these two ionic liquids were selected to be combined with conventional alkanolamine solvents, namely Monoethanolamine (MEA), Diethanolamine (DEA), and Methyl Diethanolamine (MDEA), in order to form hybrid solvents. P-T-x data was obtained for CO2 absorption in alkanolamine-ionic liquid hybrid solvents containing various compositions of the above alkanolamines and ionic liquids, by gravimetric analysis, under temperature and pressure conditions as described above. CO2 absorption in the hybrid solvents was analysed, compared, and benchmarked against absorption in pure ionic liquids and conventional alkanolamine solvents. Absorption data for pure ionic liquid systems was modelled using the Redlich-Kwong equation of state (RK-EOS), while absorption in hybrid solvents was modelled using the RK-EOS for the ionic liquid components and the Posey-Tapperson-Rochelle model for the alkanolamine components of each hybrid solvent. All modelling was programmed using MatlabTM R2012B engineering programming software. Further composition analysis was intended using Fourier transform infrared (FTIR) spectroscopy. The design and development of this apparatus is described herein. The apparatus possessed limitations in achieving the desired measurements. Recommendations are described for future modifications to make the apparatus more applicable for the systems in this work. The most important conclusion was that the hybrid solvents successfully achieved higher equilibrium CO2 absorption than conventional alkanolamine solvents and pure ionic liquids, at low pressure. Absorption increased with higher temperature, lower pressure, and alkanolamine concentrations lower than 40wt%. Modelling of CO2 absorption in hybrid solvents using the above stated model proved inadequate, with deviations nearly as high as 10% of measured data. A process of CO2 capture was simulated using the engineering software Aspen Plus V8.0. CO2 absorption in the hybrid solvent containing MEA:DEA:[Bmim][BF4] at 31.8:12.1:56.1 wt% was benchmarked against CO2 absorption in a conventional alkanolamine solvent. The simulation revealed a significant improvement in CO2 absorption using the hybrid solvent at low system pressure. However CO2 selectivity and solvent recycle heat duty results were undesirable. Finally, recommendations are listed for future research endeavours, simulation and apparatus development.
Cellulose nanocrystals: plant design for up-scaled production and applications in green construction materials.
(2021) Roopchund, Rishen.; Andrew, Jerome Edward.; Sithole, Bishop Bruce.
Two main problems were addressed in this project. Firstly, upscaling technologies from the laboratory scale to industrial scale is difficult in the absence of pilot scale facilities. This research entailed the development of upscaling protocols for large scale production of cellulose nanocrystals (CNC) from sawdust waste biomass to meet increasing end-user demands at the Biorefinery Industry Development Facility (BIDF). Secondly, despite CNC having excellent properties for potential applications in high performance products and materials, CNC applications are still in their infancy, thus needing the demonstration of high impact applications. To propose potential solutions to these problems, the purpose of this research was to firstly design up-scaled CNC production plants with production capacities ranging from 1 kg/day to 1000 kg/day. These upscaling protocols will ease the difficulty of upscaling the CNC production from the laboratory scale to industrial scale without pilot scale facilities. The second research purpose was to demonstrate the application of CNC in novel green construction materials. The widespread use of ordinary Portland cement (OPC) in the construction industry, and the current landfilling of fly ash are environmentally-degrading. Hence, the CNC-enhanced novel green construction materials used fly ash as a precursor to potentially replace OPC in the construction industry. Furthermore, a database of the mechanical, electrical, thermal, and microstructural properties of the novel green construction material was produced to guide further research and optimizations. Additionally, a universal iterative empirical framework was produced to develop novel green construction materials, whose properties can be customized per the requirements of the target application. Based on the two main research purposes, the dissertation was divided into two parts: Part A dealt with the up-scaled CNC production process design, and Part B dealt with the application of CNC in the development of novel green construction materials. Regarding the research design and methodology, the Project Life Cycle Management framework commonly applied in Industry, in conjunction with literary design standards and guidelines, were used in the process design. Software simulations were also used for certain aspects of the process design. The CNC production process design included a de-mineralization (process) water plant and an acid recovery plant. The equipment sizing and degree of automation were different for each production scale. For the development of the novel green construction material, meta-analyses coupled with statistical experimental design were used to optimize the experimental trials. The mechanical and electrical test results were used to generate three-dimensional response plots of the CNC effects, thus forming the property database. CNC was found to improve the strength, density, and corrosion resistance (dictated by the electrical resistivity) of the fly ash-based geopolymer construction materials produced at small quantities (optimally 1.7% by volume) when cured for 48 hours with sample rotation. The geopolymer exhibited endothermic properties based on the heat flow analysis, implying its suitability in thermal resistance applications. Furthermore, higher CNC concentrations were found to induce thermal stability during thermal variations in the curing and elevated temperature exposure. Overall, the application of CNC in green construction materials and the empirical framework for the custom development of green construction materials showed substantial potential, thus holding the ability to improve the commercial viability of novel green construction materials to improve their competition against OPC. The study concluded that the up-scaling protocols developed for CNC production from sawdust waste biomass can be applied in the absence of pilot scale facilities. Furthermore, this study demonstrated that CNC can be applied to develop high performance green construction materials. Only small quantities of CNC (less than 0.5% concentration) were required to improve the thermal and mechanical properties of the novel green construction materials. These small CNC concentrations yielded compressive strengths of up to 8000 kPa and generally reduced the mass loss of samples when exposed to elevated temperatures up to 7%. The broader implication of this project is that the implementation of the desired up-scaled CNC production plant can create employment and boost the economy while providing a steady supply of CNC to meet the growing end-user requirements. Furthermore, the two environmental issues of unsustainable industrial waste disposal and unsustainable OPC building materials can be solved by applying suitable industrial waste materials to produce novel green construction materials as alternatives to OPC using the empirical framework provided in this work.
Changes in the chemical composition of sugar cane (Saccharum officinarum) during storage.
(1973) Bruijn, Jacob.; Sutton, Donald A.; Matic, M.
An outline is given of the South African sugar industry, with particular emphasis on the unit operations which make up the industrial process for manufacturing sugar from cane. Current knowledge of the chemistry of soluble polysaccharides is reviewed and the structures of several polysaccharides, including starch, dextran, and pullulan, are discussed. It has been found that changes take place in the chemical composition of the juice in sugar cane (Saccharum officinarum) during post-harvest storage. With increasing storage time, there is a proportional decrease in the starch content of the juice, and a considerably larger proportional increase in the soluble polysaccharide content. The increased polysaccharide content was found to be due to a single glucan which, contrary to most previous publications on this subject, is definitely not a dextran. Following structural analysis, it has been established that the polysaccharide formed in stored cane had not been described before and the name "sarkaran" , derived from the Sanskrit word "Sarkara", meaning "sugar" is proposed for it. The polysaccharide was isolated from cane juice by precipitation with ethanol after the starch in the juice had been removed by centrifugation. The polysaccharide was purified by repeated dissolution in water and reprecipitation with ethanol. Analysis by gel chromatography resulted in a single symmetrical peak, indicating that the isolated polysaccharide is homogeneous. This was confirmed by hydrolysing fractions representing a section of the ascending and a section of the descending part of the peak of the chromatogram, using the enzyme pullulanase. Chromatographic separation and quantitative analysis of the isolated oligosaccharides showed that the compositions of the two enzymes digests were identical. Acid hydrolysis of the polysaccharide resulted in a single hexose. This was identified as glucose by paper chromatography, comparing the Rf value with that of pure glucose. Confirmation was obtained by comparing the osazone with that of glucose, using microscopic examination and determination of the melting points. Paper electrophoresis showed the molecule to be uncharged. Several techniques, both absolute and non absolute, were used to determine the molecular weight of the polysaccharide. A method involving viscosity determination indicated a molecular weight of 34 000 while a figure of 50 000 was obtained by gel chromatography on a Sephadex column, comparing the peak elution volume of the polysaccharide with that of dextrans of a defined molecular weight. Both these techniques are non absolute and yield rough estimates of the molecular weight. Osmometric measurement, an absolute method, showed the number average molecular weight to be 51 500. An absolute value for the weight average molecular weight of 250 000 was obtained by light scattering techniques. Data from the light scattering experiments were also used to determine a value of 200 - 250 A for the radius of gyration RG of the polysaccharide. End group analysis after exhaustive methylation resulted in a value of 24 000 for the number average molecular weight Mn. This indicates either that some degradation of the polysaccharide molecule occurs , during the methylation procedures or that there is a certain degree of association between individual molecules. Periodate oxidation showed that 32 percent of the glucosidic linkages are in ( 1 + 6 ) position. The polysaccharide was exhaustively methylated by several Haworth methylations followed by a number of Kuhn methylations. The fully methylated product was methanolysed and the methyl glucopyranosides analysed by gas liquid chromatography. The results were compared with those obtained from fully methylated starch and dextran. From the absence of disubstituted methyl derivatives in the methanolysate it was concluded that the polysaccharide is an unbranched glucan. From the quantities of Methyl 2,3,4,6 tetramethyl-O-Dglucopyranoside, Methyl 2,3,6, trimethyl-O-D-glucopyranoside and Methyl 2,3,4? trimethyl-0-D-glucopyranoside, it was concluded that the only linkages in the glucan are ( 1 + 4 ) and ( 1 + 6 ) and that these are present in the ratio 68:32. Enzymic hydrolysis, using pullulanase, was followed by paper chromatographic separation. Quantitative determination of the oligo-saccharides present in the enzyme digest resulted mainly in two oligosaccharides, maltotriose and maltotetraose, in nearly equal proportions. For this reason it was postulated that the polysaccharide is a maltotriose-maltotetraose polymer, and that the individual units are linked in ( I + 6 ) position, a linkage for which pullulanase is specific in certain configurations. The sequence of the maltotriose and maltotetraose units in the polymer has not been investigated further, although this could be carried out by partial acid hydrolysis, followed by isolation and identification of the various oligosaccharides formed. An alternate method for the determination of the sequence of the monomers is discussed. It was subsequently shown that the linkages in the polysaccharide are in the a configuration. The polysaccharide is highly dextra rotary and the magnitude of the rotation is comparable to that of other polysaccharides linked in a position, . such as starch and dextran. Infrared spectroscopy was used to confirm the configuration. The spectrogram of the polysaccharide contained an absorption peak at 840 cm-1 , which is typical of the a-anomeric absorption occurring, for example, in the IR spectrum of starch. The spectrogram exhibited no absorption peak at 891 cm-1 , the wavelength typical of the B-anomeric absorption in the IR spectrum of cellulose. In addition, it was found that all polysaccharides containing a ( 1 + 4 ) linkages show an absorption peak at 700 cm 1. This absorption peak was absent in all IR spectra obtained from various dextrans. This phenomenon has not been reported previously and it is suggested that the presence of this absorption peak in the IR spectrum of a glucan can be used to support the evidence of the presence of a( 1 + 4 ) linkages. It was not possible to correlate the formation of the polysaccharide with the occurrence of a specific micro organism. It is suggested that the formation of the polysaccharide is the result of enzymic reactions in the sugar cane after harvesting. The investigation of the composition of juices from deteriorated cane has not been confined to polysaccharides. Ethanol has been isolated from the juice of some samples of stored cane which had been burnt before harvesting. The ethanol was isolated by fractional distillation and identified by measurement of the boiling point. It was confirmed, by the formation of the molybdate-xanthate complex, that the product isolated was an alcohol. The identification was further confirmed by oxidising the ethanol to acetic acid and proving the identity of the acids by paper chromatography. It has been shown that, with the exception of two acids, the carboxylic acid composition of cane juice remains unaltered during post-harvest storage of the cane. The two exceptions , succinic and aconitic acids, were identified from their melting points and by specific spot tests. Ion exchange was used to isolate the acids from the juice. The eluate from the ion exchange column was concentrated and the acids separated by liquid-liquid chromatography, using a silica gel column. The levels of both aconitic and succinic acids were found to increase during the early period of storage but decreased again slowly thereafter. The percentage change was greater in the case of succinic acid, although aconitic acid was the most abundant carboxylic acid in the juice. Lactic acid was absent from the cane juices analysed. This is surprising, as lactic acid is a common product of the metabolism of carbohydrates by micro organisms. It is suggested that the changes in acid composition during the storage of harvested cane are caused by deactivation of enzymes of the Krebs cycle. Post-harvest deterioration of sugar cane can have serious consequences which can affect the whole Sugar Industry. Not only is crystallisable sugar lost but the products of the deterioration have adverse effects on factory processing and laboratory analysis. The problem, which will become more acute with the introduction of mechanical cane harvesting, can only be resolved through the cooperative efforts of all the parties concerned.
Characterization and analysis of keratinous material from waste chicken feathers as protein ingredient for animal feed.
(2022) Kekana, Lizzy Mpho.; Sithole, Bishop Bruce.; Govinden, Roshini.
Keratin is one of the most abundant proteins, which is derived from wool, feathers, nails, hair, and other sources. Chicken feathers are a well-known keratin waste by-product, produced in large quantities by poultry slaughterhouses. Their disposal is expensive, and includes incineration of the waste thus contributing to greenhouse gases; or disposal in landfills, also leading to environmental pollution or they can be recycled into low-quality feeds for animals. Research is done worldwide for the beneficiation of waste chicken feathers into commercial products; these include cosmetics, pharmaceutical products, and biomedical products, and it is also useful in the production of animal feed. The focus of this research was to characterize and analyze keratinous hydrolysates formed from waste chicken feathers using enzymatic and chemical hydrolysis for their suitable applications in different industries. The novelty of this project is based on looking at analytical techniques of the keratinous hydrolysate produced from newly formed keratinolytic microorganisms and newly optimized chemical methods from the waste chicken feathers. Different fungal and bacterial strains were tested for the degradation of waste chicken feathers. The quality and quantity of the hydrolysate formed were determined by using a combination of analytical techniques, where the characterization is done via proximate and ultimate analysis. We used Fourier Transform Infrared Spectroscopy (FTIR), which showed the presence of the keratinous structure, which is known to have high protein content. Thermogravimetric Analysis (TGA), showed that a thermally stable hydrolysates were obtained, which is known to be formed by the hydrophobic hydrolysate, which is best for animal feed. CHNS analysis showed evidence that we have high protein content in the hydrolysate. Bradford assay revealed different quantities of the hydrolysate while Sodium Dodecyl Sulphate–Poly-Acrylamide Gel Electrophoresis (SDS-PAGE), showed mostly medium to low molecular weight, due to the presence of amino acids and small peptide chain. A low Ash Content was obtained which means a cleaner fraction of keratin. The hydrolysate formed from the enzymatic hydrolysis contains a mixture of amino acids and peptides. These peptides and essential amino acids formed are known to play a special role in various biological activities. The hydrolysates formed from different degradation methods were also compared, focusing on the qualities and quantities formed from enzymatic and chemical hydrolysis. While looking at all the characterization techniques, enzymatic was the best and suitable for animal feed due to the obtained keratin structure, which is more soluble, contains high protein content, has low molecular weights, and has a cleaner fraction of keratin. Future work will be based on obtaining a peptide chain using Liquid Chromatography with tandem Mass Spectrometry (LC-MS/MS), then testing the hydrolysates for bioactivities.
The Chemical removal of sulphates using barium salts.
(1988) Trusler, Graham Errol.; Buckley, Christopher Andrew.; Edwards, R. I.; Brouckaert, Christopher John.
Abstract available in PDF copy.
Comparison between air drying and steam drying in a fluidized bed.
(1991) Faber, Ernest F.
No abstract available.
A comprehensive investigation of existing sanitation helminth enumeration methods with the aim of producing an international standard.
(2022) Naidoo, Danica.; Archer, Colleen Edith.
TeHelminth testing in faecal sludge should be consistent so data are comparable. New faecal sludge treatments for on-site toilet technologies are constantly being developed in order for municipalities in developing countries to supply dignified alternatives to sewered systems that waste large amounts of potable water and require pumping to wastewater treatment works for centralised treatment. In order to ensure that these new, onsite toilet technologies adequately sanitise the faecal matter, helminth eggs are spiked into these systems to test inactivation according to the ISO-30500 standard for non-sewered sanitation systems (NSSS). A sensitive, standard helminth isolation and enumeration method, accredited to the ISO-17025 international standard for testing and calibration laboratories, is therefore required for application in laboratories globally. Internationally, laboratories and groups have used variations of the standard United States Environmental Protection Agency (USEPA) Method (2003), the Mexican Standard for Wastewater Analysis (2012), the Bailenger Method (1996) and the Pollution Research Group (PRG) Helminth Method (2017) previously used by the Water, Sanitation and Hygiene Research and Development Centre (WRDC) for helminth testing, and formed the foundation of this study. Conventional helminth methods can be broken down into five steps: washing and sedimentation of samples to separate eggs from larger particles, flotation using density gradients to separate eggs from heavier particles, centrifugation after both washing and flotation, extraction, that involves the use of a buffer and solvent combination to further separate organic material from eggs, and microscopic analysis. Some methods also include incubation that allows for egg-viability assessment. Every reagent used in these helminth methods was tested on Ascaris suum eggs for varying time intervals; ammonium bicarbonate and 7X® (a brand of ionic surfactant) performed best in terms of egg development and viability. Washing samples under pressure and no pressure were compared and the former produced the best egg recovery. Different flotation solutions were tested at different specific gravities, and zinc sulphate at specific gravity of 1.3 recovered the most eggs. Centrifugation speeds and times were tested after the washing and flotation steps, and 3000 rpm for 10 minutes and 2000 rpm for 15 minutes produced optimal egg recovery, respectively. Different extraction combinations were tested, and it was discovered that eggs were lost in this step. It was therefore recommended that extraction be removed from the method. Different wash solutions were then tested against various sample types to determine which resulted in the highest percentage egg recovery and which solutions facilitated easier microscopic analysis. Based on data from each experiment, a final SOP was produced for the new WRDC Helminth Method, that accommodates different sample types and egg viability assessment post incubation.st method.
Decentralised sanitation to fill the gap in urban wastewater treatment within the eThekwini Municipality: a focus on tertiary treatment in vertical down-flow constructed wetlands.
(2022) Arumugam, Preyan.; Pocock, Jonathan.; Brouckaert, Christopher John.
South Africa’s bulk sanitation infrastructure is failing, and there is an urgent need to look at other appropriate sanitation solutions. Moreover, there is no data on the proportion of population with access to safely managed sanitation services, an indicator for the United Nation’s Sustainable Development Goal (SDG) 6.2.1a. In a safely managed sanitation service, the user is provided with an improved facility, not shared with other households, and the excreta is safely disposed in situ or transported and treated off-site. In the city of eThekwini, informal settlements spring up faster than services can be delivered, severely impacting on public health, the environment, and the social well-being of these communities. The eThekwini Municipality sees the benefits of decentralised sanitation solutions for in situ informal settlement housing upgrades, but the selected system needs to produce fully compliant effluent with the Department of Water and Sanitation’s (DWS) Revised General Authorisation (GA) limits for safe discharge to a water resource. Since 2010, a modular-designed demonstration-scale decentralised wastewater treatment system (DEWATS) for raw domestic wastewater from 84 households has been in operation in eThekwini. The DEWATS operates with no electricity or chemicals for treatment, but was designed according to European best practice, and not according to the community served (such as influent characterisation and hydraulic loading). This study evaluated the applicability of vertical downflow constructed wetlands (VFCWs) as the tertiary treatment module in DEWATS in four design configurations, to determine an appropriate design that can be applied for the formal housing upgrades where safe discharge of the final effluent is required. These designs, all receiving anaerobically treated domestic wastewater from the demonstration-scale DEWATS and operating in the field, were: 1. A single-stage demonstration-scale VFCW (design 1) compared to its hybrid configuration with a horizontal flow CW (HFCW) (design 2). 2. VFCWs with extended filter depths (1 m) consisting of 2-3 mm coarse sand media (at pilot-scale) (design 3). 3. Two-stage VFCWs (at pilot-scale, operating under field conditions) (design 4): a. First stage: 0.5 m filter depth consisting of 2-3 mm coarse sand media. b. Second stage: 0.6 m filter depth with 0.5-2 mm fine to coarse sand media. Neither design was able to produce fully compliant effluent for safe discharge to a water resource. Depth had no impact on the treatment efficiency of the pilot-scale single-stage VFCWs; although the design with a two-stage VFCW, adapted from the Austrian design, did achieve higher total nitrogen removal compared to single-stage VFCWs with/without extended filter depths. Overall, design 2 with the demonstration-scale hybrid CW design (VFCWHFCW) produced the highest quality effluent. However, nitrate-N removal was limited in the HFCW due to low residence times, mixed aggregate media, high dissolved oxygen (DO) concentrations and lack of available carbon as an energy source for denitrification. A plantbased carbon source from dried plant material of the invasive Giant reed, Arundo donax L., was used to augment the carbon availability for denitrifying bacteria within the HFCW. However, it is surmised that the DO concentration above 0.5 mg L-1 limited NO3-N removal. It is recommended that the DEWATS design with the hybrid CW system be redesigned according to the raw wastewater characterisation and media gradation within both CWs to ensure sufficient residence times, natural aeration in the VFCW, limited diffusion of oxygen into the HFCW, and increased availability of biodegradable chemical oxygen demand carbon for denitrification. Moreover, if the upgraded households are installed with urine diversion flushing toilets, then the nutrient load to the DEWATS will be reduced, potentially resulting in fully compliant effluent. Consequently, DEWATS will then be considered a safely managed sanitation service, allowing South Africa to track their progress against SDG 6.2.1a.
Design and operation of a multistage pressurized fluidized bed combuster.
(1981) Eleftheriades, Christos Mimi.
A three-stage Pressurized Fluidized Bed Combustor (PFBC) of principal dimensions, O,4Sm internal diameter by4m high was designed and fabricated to burn South African coals, with particular reference to coals unsuitable for burning in conventional boilers. The combustor which is the first of its kind and probably one of very few operational PFBCs in the world, was made of three jacketed sections positioned vertically one above the other and bolted together at the flanges. Distributor plates were located at the flanges which gave the combustor a multistage capability. A three, two, or one deep Fluidized Bed (FB) configurations were possible by removing the interstage distributors. Interstage solids circulation was made possible by the use of downcomers transporting solids downwards between the FBs. The solids were returned to the top FB using a pneumatic conveyor. The design of the PFBC was a sequence to a series of experimental and theoretical investigations which were carried out in order to provide us with the necessary PFBC design parameters. These investigations dealt with the following areas of research: (a) the development of a new type of cyclonic tuyere capable of transmitting through it high quantities of solids with the fluidizing gas, without choking, (b) the transfer and control of the downward flow of solids through downcomer pipes, (c) the control of the circulation of solids in a Circulatory system using a non-mechanical solids flow control valve, (d) the development of a new type of start up burner which could operate immersed under the solids, and (e) the combustion of coal in a small FB under batch conditions and the study of reaction kinetics of South African coals. On the basis of the results of the investigation in these research areas and the findings of research of individuals and of .organizations working in the field of fluidization technology the PFBC was designed, built, and successfully commissioned. A series of 12 runs, with each run lasting between 2 and 8 days, totalling more than 1500 hours, were carried out on the PFBC. Char and coal with ash content between 30 and 70 per cent were burnt in the combustor using various combinations of feeding ports and number of FBs. System pressures ranged between atmospheric and 6 bar(abs). For some of the runs the reactor was operated in a counter-current mode with solids and combustibles descending against the upflowing fluidizing air in order to study the effect that counter-current flow had on the efficiency of combustion. The combustion trials showed that the two-FB combustor, operated preferably without solids circulation, with the bottom FB acting as the main combustion cell and the top FB as a smuts burn-out cell, proved to be the most practical and most suitable combustor for burning South African high ash coals and fines or, in general, any low-grade carbonaceous materials of any size. With this configuration combustion efficiencies of up to 99 per cent, based on the combustibles in the feed and the ash, were achieved. The department computer (COC1700) was successfully linked with the PFBC for real time data logging and data processing. A mathematical model which was based on our research findings and the work of T.P. Chen and S.C. Saxena, C. Fryer and O.E. Potter, and D. Levenspiel was successfully developed and applied to the twoFB PFBC. The model describes the devolatilization and combustion of coal particles in the FB in accordance with a shrinking core type model and uses a population balance over all particles for the overall mass balance. The results from this model, which was put onto the computer, compared favourably with the experimental results and the model can be confidently used to predict the behaviour of the PFBC. It can also be easily adapted for use on any other single or multifluidized bed reactors provided that the assumptions made for the derivation of this mathematical model still hold. A mathematical model based on the work of H.C. Hottel and A.F. Sarofim, and L. Wender and G.T. Copper was also developed. This model describes the transfer of heat from the FB to the cooling coils using a stepwise heat and mass balance along the length of the cooling coil. Although this mathematical model was developed specifically for the cooling coils of our combustor it is strongly believed that it can also form the basis of a general purpose model.
Design of a static micro-cell for phase equilibrium measurements : measurements and modelling = Conception d'une micro-cellule pour mesures d'é́́́quilibres de phases : mesures et mod́élisation.
(2011) Narasigadu, Caleb.; Ramjugernath, Deresh.; Naidoo, P.; Coquelet, Christophe.; Richon, Dominique.
Vapour-Liquid Equilibrium (VLE), Liquid-Liquid Equilibrium (LLE) and Vapour-Liquid-Liquid Equilibrium (VLLE) are of special interest in chemical engineering as these types of data form the basis for the design and optimization of separation processes such as distillation and extraction, which involve phase contacting. Of recent, chemical companies/industries have required thermodynamic data (especially phase equilibrium data) for chemicals that are expensive or costly to synthesize. Phase equilibrium data for such chemicals are scarce in the open literature since most apparatus used for phase equilibrium measurements require large volumes (on average 120 cm3) of chemicals. Therefore, new techniques and equipment have to be developed to measure phase equilibrium for small volumes across reasonable temperature and pressure ranges. This study covers the design of a new apparatus that enables reliable vapour pressure and equilibria measurements for multiple liquid and vapour phases of small volumes (a maximum of 18 cm3). These phase equilibria measurements include: VLE, LLE and VLLE. The operating temperature of the apparatus ranges from 253 to 473 K and the operating pressure ranges from absolute vacuum to 1600 kPa. The sampling of the phases are accomplished using a single Rapid-OnLine-Sampler- Injector (ROLSITM) that is capable of withdrawing as little as 1μl of sample from each phase. This ensures that the equilibrium condition is not disturbed during the sampling and analysis process. As an added advantage, a short equilibrium time is generally associated with a small volume apparatus. This enables rapid measurement of multiple phase equilibria. A novel technique is used to achieve sampling for each phase. The technique made use of a metallic rod (similar in dimension to the capillary of the ROLSITM) in an arrangement to compensate for volume changes during sampling. As part of this study, vapour pressure and phase equilibrium data were measured to test the operation of the newly developed apparatus that include the following systems: • VLE for 2-methoxy-2-methylpropane + ethyl acetate at 373.17 K • LLE for methanol + heptane at 350 kPa • LLE for hexane + acetonitrile at 350 kPa • VLLE for hexane + acetonitrile at 348.20 K New experimental vapour pressure and VLE data were also measured for systems of interest to petrochemical companies. These measurements include: • VLE for methanol + butan-2-one at 383.25, 398.14 and 413.20 K ABSTRACT • VLE for ethanol + butan-2-one at 383.26, 398.23 and 413.21 K • VLE for ethanol + 2-methoxy-2-methylbutane at 398.25 and 413.19 K • VLE for ethanol + 2-methylpent-2-ene at 383.20 K These measurements were undertaken to understand the thermodynamic interactions of light alcohols and carbonyls as part of a number of distillation systems in synthetic fuel refining processes which are currently not well described. Two of these above mentioned systems include expensive chemicals: 2-methoxy-2-methylbutane and 2-methylpent-2-ene. The experimental vapour pressure data obtained were regressed using the extended Antoine and Wagner equations. The experimental VLE data measured were regressed with thermodynamic models using the direct and combined methods. For the direct method the Soave-Redlich-Kwong and Peng-Robinson equations of state were used with the temperature dependent function (α) of Mathias and Copeman (1983). For the combined method, the virial equation of state with the second virial coefficient correlation of Tsonopoulos (1974) was used together with one of the following liquid-phase activity coefficient model: TK-Wilson, NRTL and modified UNIQUAC. Thermodynamic consistency testing was also performed for all the VLE experimental data measured where almost all the systems measured showed good thermodynamic consistency for the point test of Van Ness et al. (1973) and direct test of Van Ness (1995).

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