In this thesis a fluidized bed containing a draft tube has been studied with the aim of developing the apparatus for coal gasification. The process has the capability of producing synthesis quality gas using air for combustion, and of being able to accomodate poor quality coal feeds containing heavy fines loads. These advantages arise from two special features of a draft tube fluidized bed. In the first place, the bed may be operated as two separate and independent reaction zones, one contained within the draft tube and the other in the annulus region surrounding it. As a result, the gasification reactions may be carried out in one compartment and the combustion reactions in the other, allowing the useful gasification products to be taken off separately and undiluted with the combustion flue gases. Secondly, the fluidized material in the bed may be induced to circulate up the draft tube and down the annulus. These circulating solids provide the heat carrier from the combustion to the gasification zones within the bed. Furthermore, circulation of the bed in this way leads to a much longer residence time of fine particles within the bed and results in a high fine coal utilization efficiency. In order to achieve these benefits in practice, it is necessary to separate the gases supplied to and emitted from the draft tube from those of the annulus, but at the same time allowing free movement of solids between these regions. The thesis deals with how this may be accomplished in three parts: Firstly, the principles underlying division of a fluidized bed with a draft tube into discrete reaction zones are formulated, and strategies for achieving zonal separation, based on these arguments, are experimentally tested. As a result a reactor configuration and operating conditions suitable for coal gasification have been empirically identified. Secondly, a model describing the bulk circulation of solid material in the bed is presented, for the draft tube operating in the slugging mode. This model allows the average solids residence time and the particle velocities in the annulus and draft tube to be predicted, provided that slug velocities and spacings are known. The necessary correlations between hydrodynamic behaviour and the system properties are available in the literature for round nosed and wall slugs, but not for square nosed slugs, which appear to be characteristic in the apparatus used here. The third part consequently examines the square nosed slugging regime, and a theory to describe this behaviour, based on interparticle stress analysis, is presented. This regime is identified as having significant advantage over other bubbling modes because of the high dense phase gas flow rates which are sustained, and the resulting improved gas-solid contacting. The three models together mathematically describe the operation of the draft tube fluidized bed, allowing gas partition between the annulus and the draft tube regions as well as solids circulation to be predicted, for different bed configurations and operating conditions. The predictions compare well with experimental results. The last part of the thesis deals with the application of the system to coal gasification on a one ton coal per day pilot plant. A high quality gas, containing up to 80% CO + H2, (balance CO2), has been produced by steam gasification in the draft tube, using air for the combustion reaction in the annulus. The H2/CO ratio can be varied from about 1 to 3, by changing the operating temperature of the reactor. / Thesis (Ph.D.)-University of Natal, Durban, 1984.

High carbon ferrochromium serves as the main chromium source for almost all chromium containing steel alloys. The traditional method for the production of high carbon ferrochromium via the reduction of chromite using coke in electric arc furnaces, draws its considerable energy requirement from electrical power. The escalation in cost of electric power in South Africa has motivated research into alternative, fuel fired, reduction processes. One such process involves the partial solid state reduction of chromite in coal fired rotary kilns at temperatures between 1200 and 140rrc, prior to electric smelting. such processes are currently operated on a commercial scale and result in considerable savings in electrical energy, despite slow reduction kinetics and low reaction extents. A large amount of research conducted in the past, . aimed at establishing the fundamentals of the reduction process, has not provided satisfactory answers to questions regarding the mechanism of reduction. It was therefore necessary to conduct further test work on the process to establish the mechanism and factors limiting the rate and extent of reduction. Thermodynamic analysis of the reaction system indicates that at temperatures above 1050C reduction of the ore will proceed, and should reach an extent of approximately 90% reduction at 1200C. Complete reduction should be achievable at approximately 125ifc. However experimental results indicate the persistence of a stable magnesiochromite spinel under normal reducing conditions even at 140ifc. This limits the degree of chromium reduction to approximately 65%. Kinetic data from thermobalance studies and electron microscope examination of the reduction product showed independent reduction of iron and chromium. The rate of iron reduction was found to be relatively rapid and to go to completion, compared to that of chromium where the formation of a relatively inert picrochromite- spinel solid solution (MgO(Cr,AI)203) at the surface of the grain liinited the rate and extent of reduction to approximately 65% in the case of LG6 chromite. These findings suggested that the only way in which the kinetics of the process might be improved was through the addition of a component capable of disrupting the spinel layer at the surface of the chromite grain. In this study, fluoride containing mixtures such as CaF2 - NaF and fluorspar- feldspar- silica were successfully used to accelerate the reaction. Such mixtures are commercially interesting and highly effective even at low additions (4- 10%) . The mechanism whereby such mixtures operate was shown to involve the dissolution of all the spinel components in the liquid flux phase. Following dissolution, rapid i i recrystallization of spinel (Mg . Al2 ~) occurs , simultaneous to the transport of Fe 2+ and cr 3+ ions through the liquid to a site where reduction can take place. The main effect of this is to increase the rate and extent of chromium reduction to the point where virtual total reduction can be achieved in less than 90 min at temperatures as low as 1200C. Although the reduction kinetics in the presence of such solvent flux phases are still largely limited by the rate of solid state diffusion, the disruption of the surface enables faster overall diffusion rates to be achieved. Ultimately as the particle size and separation between oxide and reductant is increased, the rate of dissolution and transport through the flux phase become rate limiting. / Thesis (Ph.D.)-University of Natal, Durban, 1989.

ABSTRACT PELCHEM, the chemical division of NECSA, produces the fluorocarbon hexafluoropropylene (HFP) onsite. In 2005 PELCHEM initiated research into the wet oxidation of HFP to produce the higher value fluorocarbon hexafluoropropylene oxide (HFPO). Although successful in the conversion of HFP to HFPO, the product stream contained both the product and the unreacted HFP. As a result, PELCHEM contracted the Thermodynamics Research Unit at the University of KwaZulu-Natal to investigate the separation of HFP and HFPO. A solvent selection procedure was used to identifY potential solvents and an initial list of two hundred and seven candidate solvents compiled. Utilising the UNIFAC group contribution method, the initial list was narrowed down to thirty solvents using the criterion of selectivity at infinite dilution. Through the comparison of specific solvent properties such as recoverability, safety, environmental factors and economic considerations, a final list of ten solvents was generated. The list of ten solvents was proposed to PELCHEM who identified four solvents for further studies. The work involving the two solvents, toluene and hexafluoroethane (RI 16), is presented in this dissertation. The solvent toluene has been previously used by the du Pont company for the separation of HFP and HFPO, while R116 is a novel solvent for this application. The solvent selection procedure was performed in collaboration with a member of the Thermodynamics Research Unit, and the work on the remaining two solvents is presented in the dissertation of (Nelson 2008). Experimental binary high pressure vapour liquid equilibrium data were measured for the HFP + toluene, HFPO + toluene, R116 + HFP, and R116 + HFPO systems at two temperatures: 273.15 and 3 13.15 K. Pure component vapour pressure data for HFPO in the temperature range of 271.90 to 318.20 K were also measured. The HPVLE measurements were performed at the Thermodynamics Energy and Phase Equilibria laboratories at Ecoles des Mines de Paris using two experimental techniques and equipment. The binary systems involving toluene were measured on a static synthetic Pressure Volume Temperature apparatus equipped with a variable volume cell. The binary systems involving RI16 were measured on a static analytic apparatus equipped with a Rapid On-line Sampler Injector. None of the systems measured for this project have been reported in the literature. The four binary systems and the pure component vapour pressure measurements thus constitute new data sets. All experimental data were modelled via the direct method using the computer software Thermopack. Three model combinations were used to represent the data: the Peng-Robinson equation of state with the Wong-Sandler mixing rules, the Peng-Robinson equation of state with the Modified-Huron-Vidal first order mixing rules, and the Soave-Redlich-Kwong equation of state with the Wong-Sandler mixing rules. The Mathias-Copeman alpha function was used in conjunction with the equation of state models, and the NRTL activity coefficient model was incorporated into the mixing rules. Due to time constraints, experimental data for the binary system HFP + HFPO were not measured. Data for this system was predicted at two temperatures, 273.15 and 313.15 K, via the PSRK-UNIFAC method. The critical line for the supercritical systems R116 + HFP and R116 + HFPO were calculated in Thermopack. PELCHEM required a commercial grade HFPO product stream of purity greater than 99 % (mole), and a purified HFP product stream of purity greater than 95 % for the recycle and conversion of HFP into HFPO. Using the regressed experimental high pressure vapour liquid equilibrium data, two preliminary separation processes were designed in Aspen Plus to achieve these objectives. The first scheme involved toluene and utilised the process of extractive distillation with toluene introduced as a liquid solvent. The toluene bonded to the HFP and was removed as a bottoms product which allowed a purified HFPO stream to be recovered as a distillate. The second scheme involved RI16 and utilised the process of gas stripping, with a liquid mixture of HFP and HFPO contacted with a gaseous stream of R116. The R116 removed the HFP from the liquid mixture, resulting in a purified HFPO stream. The toluene process resulted in an overall HFPO product recovery of 98.46 % and HFPO product purity of99.88 % (mole). The RI16 process resulted in an overall HFPO product recovery of96.57 % and HFPO product purity of99.71 %. For the component HFP, the toluene process resulted in an overall HFP product recovery of 99.42 % and product purity of96.41 %. The RI16 process resulted in an overall product recovery of99.36 % and product purity of93.45 %. From a comparison of the preliminary design of the separation processes on the basis of patent issues, performance, and other miscellaneous factors, it was concluded that the RI16 process compared favourably to the process involving the solvent toluene. The preliminary process designs were presented to PELCHEM in 2007, and pending further experimental work PELCHEM plans to patent the RI16 separation process. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2008.

The gas phase polyethylene production process is the most recently developed and boasts many / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2006

No abstract available. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2006.

South Africa has an annual sugarcane milling capacity of about 22 million tonnes on average producing about 3.3 million tonnes of dry bagasse, of which one third is surplus to factory requirements. Currently surplus bagasse is used for furfural, pulp and paper and cogeneration but significant amounts still remain . This prompted the need to find viable alternative and appropriate technology to utilize the surplus. A laboratory pilot plant was used to investigate the production of activated carbon from bagasse. Experiments were carried out to investigate conditions for making the best activated carbon in a rotary batch kiln, and also to examine potential ene rgy recovery from process gases using Gas Chromatography. Derived results from the laboratory experiments were used to develop a conceptual design for a demonstration plant sited within a sugar mill. The conceptual design was evaluated for economic and environmental impacts using a robust Excel spreadsheet and GABI-3 modelling software respectively. Excellent activated carbon was produced from sugarcane bagasse by a two-stage physical process involving pyrolysis and gasification with steam. The best operating conditions were pyrolysis at 700°C for 1 hr and activation at 850°C for 1hr, a heating rate of 10°C/min and a steam flow of 15g/g of char per hour. The active carbon yield was 7% on dry bagasse basis with a Methylene Blue Number of 257mglg of carbon. The active carbon had a sugar decolourisation capacity of 20% at a carbon dosage rate of 0.7 wt% on Brix using clear juice (l2°Brix) and 70% at 0.5 wt% on Brix using brown liquor (65°Brix) . The Freundlich isotherm showed that the bagasse-based activated carbon was a suitable adsorbent for sugar colour bodies. Gas analysis results revealed that the off gases from the pyrolysis and activation stages had calorific values of about 63MJ and 31MJ per kg of activated carbon respectively . The total combustion energy of 94 MJ/kg of active carbon was enough to satisfy the process energy requirements for drying, pyrolysis and activation. By burning combustibles like tar, methane, carbon monoxide, ethylene and hydrogen for process thermal energy needs, the environmental impact of the manufacturing process was reduced to a Global Warming Potential of llkg CO2 Equiv per kg of carbon produced. The demonstration plant requires a capital investment of US$lOA million to give a competitive bagasse-based activated carbon (BPAC) selling price of US$1.80 per kg and IRR, ROI and Investment payback time of 17.93%, 23.93% and 3.80 years respectively. A sensitivity analysis was also carried out to investigate the effect of possible variation in the main project forecasts which are BPAe selling price , bagasse buying price, capital investment and production costs on IRR, ROI and payback time . The benefits of process integration within a sugar mill would be expected to improve the business feasibility ; If bagasse was free the IRR would increase to 28.59% and even better to 32.12% if extra boiler and electricity capacity was also available at the mill. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2005.

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. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2007.

In this study, there was a need for VLE data for systems of oxygen-containing organic compounds. Experimental VLE data are presented for the following binary systems: a) 2-propanone (1) + 2-butanol (2) at 333.15K, 353.15K and 373.15K b) 2-propanone (1) + n-propanoic acid (2) at 333.15K, 353.15K and 373.15K c) 1-propanol (1) + n-butanoic acid (2) at 333.15K and 353.15K A test system (cyclohexane + ethanol at 323.15K) was measured to confirm the accuracy of the method and apparatus. With the exception of the test system, data for all the other binary systems investigated in this study are currently not available in the open literature. The dynamic recirculating stills of Joseph (2001) and Reddy (2006) were utilised to undertake the measurements. The experimental vapour pressure data measured in this study and the results obtained for the highly non-ideal test system were in excellent agreement with the literature data. It was thus concluded that the apparatus and operating procedures used were capable of producing highly accurate VLE data and confidence in the new data measured was obtained. Thermodynamic consistency testing was performed on the experimental VLE data using the point test (Van Ness et al., 1973), which provided an indication of the data’s quality and reliability. The data were thereafter subjected to data correlation to enable interpolation of the data and extrapolation to conditions other than those measured. Appropriate thermodynamic models (taking into account vapour-phase association in particular) were correlated to the data using the combined approach to VLE ( - method). For the calculation of the fugacity coefficients, three methods were used viz. the virial EOS and the Hayden-O’Connell correlation (1975); chemical theory and the Nothnagel et al. Formulation (1973); and the VPA/IK-CAPE EOS (Abbott and Van Ness, 1992). Three activity coefficients models were also used viz. the Wilson (1964) model; the NRTL model (Renon and Prausnitz, 1968); and the UNIQUAC model (Abrams and Prausnitz, 1975). In general, the models fitted the data well and the model parameters that were acquired are included. Theoretical developments involving associating components are ongoing. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2009.

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. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2013.

South Africa is the world’s largest producer of platinum group elements (PGEs). Mining takes place in the Bushveld Complex, and recent statistics, (Mudd, 2010), showed that the UG2 reef is the main source of production, accounting for approximately 60% of world mining production. However, recovery by flotation is complicated by variations in the mineral composition, the need to grind fine and entrainment of chromite, which has an adverse effect on the subsequent smelting of the concentrate. The recovery of PGEs is variable, and it is influenced by PGE feed properties such as degree of liberation, mineral type and grain size. Conventional rougher batch flotation tests on drill core samples do not provide sufficient information for predicting plant performance. The aim of this research was to develop a rigorous method for the testing of UG2 drill core samples. A rougher-cleaner flotation test procedure was developed, and statistical tests were applied to select an appropriate model, which included entrainment of hydrophilic minerals. Fifty UG2 samples from across the Bushveld were milled at a fixed energy input, and the new test procedure was applied to derive model parameters for all samples. There was a significant variability in the PGE recovery, and typical feed characteristics such as PGE feed grade and grind did not show a clear link to the PGE recovery. This was due to the complex mineralogy of the PGE minerals and variations in ore hardness. Hence, a statistical modelling algorithm was used to determine the factors affecting PGE recovery, and an empirical model was developed, which relates the PGE recovery to feed properties. The model can be used to estimate PGE recovery based on feed properties. Samples which had a high base metal content (e.g. high nickel to iron ratio) had a high PGE recovery, and samples which were altered (e.g. high Rb/Sr ratio and loss on ignition) had a low PGE recovery. Depressant addition is used in PGE flotation to control the recovery of gangue, but it also affects the flotation of composite PGE/gangue particles. Seven of the fifty UG2 samples were selected for a more detailed investigation, using a more advanced batch flotation test and a mineralogical liberation analysis. The advanced batch flotation test was a new development, in which flotation model parameters were derived simultaneously for flotation after two stages of grinding and a combined cleaning stage. The effect of a range of depressant additions was also modelled. The floatable PGE fraction, determined from batch modelling, was linked to the mineralogical liberation analysis of the feed. The model is the first of its kind, and it makes it possible to predict the mineralogical characteristics of the feed from flotation data. A spread-sheet simulator was developed, to demonstrate how batch data (from the advanced flotation test) could be used to predict plant performance. Scale-up parameters were derived by using pilot-plant data for one of the ores. The spread-sheet was then used to optimise the plant design and depressant addition for an ore, while constraining, the mass of concentrate and the chromite content. The example showed that there was an optimum depressant addition and rougher-cleaner volume capacity for an ore. The gambit of this study was the linking of feed chemical assay and mineralogical properties to PGE recovery. The application of mineralogical tests and modelling of data from the advanced flotation test has demonstrated that the link is relatively complex. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2013.