Browsing by Author "Petrie, Jim"

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    A first order assessment of the moving granular panel filter
    (1987) Shaw, Gareth D. H; Petrie, Jim
    The capabilities of a specific moving granular panel bed filter are investigated, highlighting FBC flue gas cleanup. The continuous operability offers some advantages over the discontinuous operating mode of the static filter bed but the effects of moving granular medium are found to introduce other disadvantages not originally anticipated. Movement of granular medium resulted in significantly reduced filtration efficiencies with respect to static granular beds for the same operating conditions. Pressure drop analysis indicated voidage increases within the bed with granular movement but the increases were not considered significant enough to explain the reduced efficiencies suffered by the moving filter medium . Reentrainment at high Stokes numbers is considered to be the main contributor for reduced filter ability. An empirical correlations was developed to model the re-entrainment effects. The causes and effects of non uniform granular flow were highlighted resolved by modification to the panel design. The modifications involved the inclination of the panel a few degrees off the vertical. The precise angle was found to depend on fluid flowrate through the filter medium. The ability of the continuous medium replenishment to maintain low fluid pressure drop was demonstrated. The concept of initial collection efficiency, used in static granular beds as a conservative measure of the filter efficiency in granular filter design, is shown not to be applicable to moving granular beds. Collection efficiencies were found to deteriorate progressively from initial clean granule conditions. Increase in panel thickness is shown to be necessary to improve the filter efficiency to that required to meet the emission regulations. The resulting increased operating pressure drop is calculated to be in the order of that imposed by an equivalent electrostatic precipitator making the design, an attractive low pressure drop filter, assuming sufficient improvement in collection efficiency can be achieved with the increased panel thickness. Order of magnitude cost estimates are presented at two different scales. Comparisons of costs with conventional filter designs show the design to be worth further investigation.
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    An assessment of the potential for waste minimisation in small and medium size enterprises in South Africa
    (1994) Coleman, Ann E; Petrie, Jim
    Against a background of a chemical engineering degree and a few years of industrial experience, I undertook this M.Sc. degree with the conviction that chemical engineering skills have a unique role to play in addressing environmental problems of pollution generated by industrial activity. Moreover, given that, of industrial activity, it is chemical processing industries (CPI) and mining industries which are the major contributors to generation of waste, hazardous waste in particular, it is appropriate that the chemical engineering profession, which populates such industry activities, should assume such responsibility. In response to increasingly vociferous demands for more stringent environmental control over industrial activity, and regulatory compliance with stricter constraints on emissions of pollutants, there is a tendency to rely on readily available end-of-pipe solutions to resolve environmental management problems. This strategy is embodied in current practices in South Africa at effluent treatment- and landfill disposal facilities. Yet this is a costly solution in the long term, with implications for increasing operating costs, investment costs for development of new facilities, as well as closure and potential liability costs for old facilities. Furthermore, this strategy fails to address problems of resource depletion and the potential for resource recovery from materials considered to be "waste". Waste minimisation offers an alternative waste management strategy which seeks to reduce the generation of waste before end-of-pipe management is required, and to recover resources for reuse, thereby reducing resource consumption. The Department of Environment Affairs in the South African government has recommended that there should be research in the application of waste minimisation. While clearly there is a need for fundamental research into particular technological problems (such research is being undertaken at some institutions), the approach I adopted was to investigate potential for effecting meaningful waste minimisation solutions using procedures and techniques which constitute popular waste minimisation assessment methodologies. I focused specifically on small and medium scale industry operators which traditionally do not employ chemical engineering skills and which need a practical tool to improve in-house environmental management capability.
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    CFD analysis of reactive crystallisation in stirred tanks : a focus on nickel hydroxide
    (2006) Krige, Andrew Richard; Petrie, Jim; Fletcher, David
    The recovery of metal values from aqueous streams via precipitation, or reactive crystallisation, is both an economically and environmentally significant unit operation in a wide spectrum of industries. However, the control and operability of these systems is hampered by the limited fundamental basis for their design, frequently resulting in downstream processing difficulties. Previous work by Dustan (2001) considered precipitaion and subsequent dewatering as an integral system, and quantified, to a first order, the relationship between the various sub-processes. The current study is aimed at further resolving the upstream components of this intergrated model (i.e. the precipitation itself), with a particular focus, due principally to the rapid kinetics typically exhibited by precipitaion systems, on mixing and representation of time-dependent spatial inhomogeneities.
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    Environmental considerations in the design of base metals refineries : metals in riverine systems
    (2003) Marr, Sean; Petrie, Jim
    There is a need for engineers involved in the desing of base metals refineries to understand the impacts of their design on the environment. Desing engineers should move their focus away from meeting effluent release concentration limits to identifying potential environmental impacts.
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    Environmental life cycle considerations for design-related decision making in minerals processing
    (1999) Stewart, Mary; Petrie, Jim
    The objective of this work is to inform environmental decision making in design for the environment in minerals processing. To this end an integrated decision hierarchy has been developed. This decision hierarchy incorporates technical, environmental and social considerations in the design process. Life Cycle Assessment (LCA) has been chosen as the metric whereby environmental considerations will be included in the decision making process. LCA information is augmented by information from the Environmental Impact Assessment (EIA) process in detailed design. There are four themes in this thesis; Minerals Processing, Process Design, LCA and Decision Making. Considerations specific to process design in the minerals industry are highlighted. The use ofLCA as a tool to assess the environmental performance of the minerals industry is discussed. LCA is then used to inform the decisions taken during process design.
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    Generalised strategy for predicting environmental characteristics of solid mineral wastes : a focus on copper
    (2007) Broadhurst, Jennifer Lee; Petrie, Jim
    The impacts associated with primary production of metallic and fossil minerals are significant, and these industry sectors are facing increasing pressure to improve environmental performance and contribute to development that is consistent with sustain ability principles. The management of large volumes of solid wastes poses a particular problem, with the potential post-closure impacts and liabilities associated with the prolonged discharge of contaminated leachate from deposits of such wastes remaining of major concern to both regulators and industry. It is only by quantitatively characterising these impacts that we can begin to focus attention backwards in the material chain to the waste generation processes themselves, and thus identify opportunities for process improvements to minimise waste formation and to render wastes environmentally benign. Whilst recognising that knowledge of the key waste properties or characteristics is an essential and integral part of quantitative environmental impact predictions, currently available data pertaining to the characteristics of solid mineral wastes are largely incomplete and inconsistent, and the mechanisms of leachate generation poorly understood. The need to improve the way in which solid mineral wastes are characterised is driven not only by the limitations in terms of current data bases and methodologies for the generation of such. There is also a requirement for a more systematic and rigorous approach, which will ensure that the necessary data and information is integrated into the early decision stages of an environmental performance assessment programme and, ultimately, project life cycle in a time and cost effective manner. It is these shortcomings and challenges that this thesis attempts to address, through the development of a generalised and systematic strategy for predicting the environmentally significant properties of solid mineral wastes on the basis of ore characteristics (waste origins) and generating processes (waste source). The conceptual approach developed within this thesis essentially entails addressing current data gaps and deficiencies through reconciliation of available empirical data with a fundamental understanding of element properties and distribution behaviour in two systematic and consecutive steps. In the first instance, solid waste characteristics are predicted from a consideration of ore type and composition (Le. waste origins), combined with knowledge of the process route from ore to waste (i.e. waste source). Due to their relevance in terms of technical and economic criteria, such as product quality and operational throughput, the behaviour of the targeted metal and major ore components in ores and beneficiation input-output streams is generally fairly well understood. Data gaps and inconsistencies pertaining to these ore components can, for the most part, be adequately addressed on the basis of meaningful generalisations and simple mass balance calculations. In contrast, available data and information relating to compositions of trace and minor co-elements are largely qualitative and inconsistent, and their deportment during the formation and subsequent beneficiation theoretical assessment of the potential distributions, properties and associations of these elements within ore deposits and across process unit operations, based on a fundamental understanding of the governing reaction mechanisms and influencing parameters. The theoretical data and information are subsequently reconciled with available empirical data to generate a comprehensive and quantitative list of potential element distribution factors which, when combined with total mass flow data, results in a first-order inventory of process input-output stream compositions. The second step of the proposed approach entails the prediction of key characteristics relating to criteria of environmental significance. In this step the solid waste constituents, identified and quantified in the first step of the methodology, are screened and ranked in accordance with their hazardous properties and availability for release to the surrounding environment in a disposal scenario. As in the case of predictions of element distributions during ore formation and beneficiation, the theoretical assessment of the potential distribution behaviour of elements from solid wastes is underpinned by a qualitative understanding of the mechanisms and parameters governing their dissolution and attenuation within a waste deposit. Potential environmental risks associated with the various solid waste constituents are subsequently estimated and compared on the basis of their total concentrations, potential environmental availability, and inherent capacity to cause harm. Three separate but inter-related case studies in the context of primary copper production present the key features of the developed approach and related tools. Such features pertain in particular to first order predictions of the chemical and mineralogical compositions of porphyry-type copper sulphide ore deposits; the subsequent distribution of ore components during concentration and smelting of the run-of-mine ores; and the waste constituents of potential environmental significance within a typical flotation tailings impoundment. Apart from addressing data gaps and inconsistencies, these case studies have also served to highlight the links in the ore formation.
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    Immobilisation of copper, chromium and arsenic on stabilised domestic refuse
    (1997) Ballard, Richard Hugh; Petrie, Jim
    The disposal of copper-chromium-arsenic, whether in solution or in combination with wood, has the potential to become a global problem. This chemical is commonly called CCA or Tanalith, and is classed as a waterborne wood preservative. Current global production of this class of chemicals is estimated at 90 000 tonnes annum-1 In South Africa (1988), the production of preservative treated wood approximates 430 000 m3annum-1 (UNEP, 1994). An experimental study to assess of the capacity of landfill biomass to adsorb (and retain) copper, chromium and arsenic waste chemicals has been carried out at laboratory and pilot scale. The work is motivated by the desire to explore the potential of domestic landfill sites to act as a final depositories for hazardous chemicals at minimal environmental risk. Copper is .present as the sulphate (copper (II)); chromium is present as dichromate (chromium (VI)); arsenic is present as the pentoxide (arsenic(V)). The laboratory scale investigation focused on the evaluation of kinetic rate constants (adsorption and desorption) and the evaluation of adsorption isotherms. At pilot-scale, the residence time distribution/deviation from ideal behaviour of the pilot-scale landfill columns was determined. Subsequently, the kinetic rate constants and the results from the residence time distribution studies were evaluated at pilot-scale. The final phase of the investigation was the application of the data obtained at laboratory and pilot-scale, to an assessment of full scale landfill practice.
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    Life cycle inventory uncertainty in resource-based industries : a focus on coal-based power generation
    (2001) Notten, Philippa Josephine; Petrie, Jim
    The aim of this thesis is to develop an approach to support prospective environmental decision-making in resource-based industries. The specific focus is on coal-based power generation. The objectives of the approach are that it be able to adequately reflect the environmental burdens arising from primary industries, and to make explicit the trade-offs often encountered in environmental decisions. In addition, it needs to take into account that the context in which the assessment takes place affects data availability and quality significantly, and consequently the certainty with which systems can be evaluated. Resource-based processes typically involve large-scale disruption of the local and regional environments, with imprecise processes and diffuse emissions. The modelling of the environmental performance of such processes therefore raises significant challenges, where many disparate sources of data, available at different levels of aggregation, and over various time intervals, have to be brought together into a coherent assessment. An "uncertain" definition of the system is therefore much more meaningful, in which variables are defined over ranges of values to cover inconsistencies and imbalances in the system. The inherently high variability of mining and minerals processes further supports their modelling as ranges of potential performance rather than "typical" operations, where the relevant process of interest must be identified and the variability within the particular process incorporated into the assessment Life cycle assessment (LeA) has received increasing attention for its role in environmental decision making processes, where it supports the process of defining the contribution of human activities to (at least the environmental dimension of) sustainable development. It is therefore the structured approach to environmental decision-making investigated in this thesis to organise the large data sets of varying quality and completeness available around resource-based industries into useful information, able to provide the environmental objective in a decision-making process. LeA is an inherently uncertain procedure in that it combines data sources of varying accuracy and representativeness, and employs subjective judgement in applying this data to future operating systems. Subjective judgements are also present in the definition of the systems, and in the modelling choices determining the accuracy and complexity of the inventory and impact models used. Nonetheless, LeA results are most often presented as single values, which in a comparative analysis, gives the often incorrect impression that one system is always better or worse than another system. A framework has been developed in this thesis to include all relevant sources of uncertainty encountered in LCA models explicitly, where empirical parameter uncertainty, model parameter uncertainty, and uncertainty in model form are investigated in a looped fashion. The innermost loop assesses empirical uncertainty in an iterative probabilistic analysis, using Latin Hypercube sampling of the uncertain input distributions to propagate the data uncertainty to the output, and rank-order correlation analyses to determine the relative uncertainty importance of the parameters input into the model. Model parameter uncertainty is assessed next, by a parametric analysis, or by a combination of sensitivity analyses and a parametric analysis, if a large number of model parameters require consideration. The top-most layer is an assessment of model form, in which alternative model forms are investigated in a sensitivity analysis.
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    Multi-agent analysis of industrial networks : a South African bio-energy case study
    (2007) Malan, Rene; Petrie, Jim
    Industrial networks are complex structures consisting of multiple interacting enterprises, differing in nature, each with independent (often conflicting) objectives, producing numerous, possibly competing products. These networks play an important role in meeting basic human needs and contributing to economic prosperity through generation, manufacture and distribution of goods and services. Design of a network to achieve more sustainable business practice requires an understanding of how its structure and function affect its economiC, environmental and social performance. In this thesis it is argued that this understanding can be gained through modelling and simulation of such networks, where existing toolkits include simulators and/or optimisers, as well as an array of "soft systems" approaches, including multi-criteria decision analysis (MCDA). An agent-based simulation-optimisation approach was developed to capture the complexity associated with modelling of industrial networks, including the decision-making process followed by each enterprise, the responsiveness and interplay between the enterprises and the evolution and performance of the network over time. This modelling approach was applied to a case study network associated with generation of electricity from biomass in the province of kwaZulu-Natal, South Africa. The network includes sugar and paper and pulp mills, the South African power utility and independent power producers. The decision-making criteria of the enterprises and the key performance indicators of the network were both measured by economic (cost and NPV respectively), environmental (C02 emissions) and social (electrification of rural communities) factors. The sensitivity of the structure and function of the network to changes in network effects (carbon credits selling price) and enterprise behaviour (decision and risk policies) was tested. It was found that changes in enterprise behaviour had the greatest influence on the structure and functioning of the network, with changes in decision policy having a greater influence than changes in risk policy. From this case study it is concluded that although each network presents custom complexities and uncertainties, the modelling approach developed in this thesis does provide a platform that allows designers, analysts and decision-makers to take into account relevant enterprise and network characteristics.
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    Predictions of leachate generation from minerals processing waste deposits
    (1995) Davies, Graham Mark; Petrie, Jim
    The minerals processing industry in South Africa produces significant tonnages of waste material which are disposed of commonly in dedicated waste depositories. These deposits pose a potential to pollute the environment if leachate is generated within the deposit and released to the surroundings. Leachate generation is generally investigated using laboratory columnar experiments which attempt to mimic the physical and chemical processes which occur in the deposit. These experiments, termed lysimeter experiments, are time consuming in that they typically last for at least a few months and can last for up to three years. Lysimeter experiments are also costly to conduct. Because of restrictions such as these, relatively few deposits have been characterised to determine the leachate which they generate and thus the risk which they pose to the environment. There is an urgent need to be able to estimate the environmental risks associated with existing waste deposits. The first step towards assessing this risk would be an ability to predict leachate generation within a specific deposit. Such an ability could be used to identify which of the existing deposits produce significant leachate and thus pose a potential hazard to the environment. Equally, if leachate generation from new deposits could be estimated as a function of waste material and characteristics of the waste deposit, this information could be used to improve the engineering design of waste deposits. The work presented in this thesis involved identifying suitable modelling strategies which could be used to determine leachate generation within waste deposits which contain waste material typical of that produced by the minerals processing industry. Two modelling strategies have been investigated. The first modelling strategy involved a macroscopic model in which all effects such as intrinsic chemical kinetics, intra-particle diffusion, external mass transfer and hydrodynamic considerations are lumped into a single parameter. The result of this approach is an effective reaction rate for the release of hazardous constituents from a volume element of the waste deposit. The effective reaction rate is determined by fitting the model to experimental data based on lysimeter tests. The main advantage of this model is that it eliminates the need for a detailed understanding of the individual factors which contribute to leachate generation. This model was investigated both for its inherent simplicity and for use in cases where insufficient information with respect to the intrinsic chemical reaction rates, intra-particle diffusion, external mass transfer or hydrodynamic aspects exist. The main disadvantage of this model is that it has a limited predictive ability in that the individual significance of any one factor which contributes to leachate generation cannot be determined. For this reason a second, more detailed model, termed the heterogenous columnar model, has also been investigated.
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    Predictions of leachate generation from minerals processing waste deposits
    (1995) Davies, Graham Mark; Petrie, Jim
    The minerals processing industry in South Africa produces significant tonnages of waste material which are disposed of commonly in dedicated waste depositories. These deposits pose a potential to pollute the environment if leachate is generated within the deposit and released to the surroundings. Leachate generation is generally investigated using laboratory columnar experiments which attempt to mimic the physical and chemical processes which occur in the deposit. These experiments, termed lysimeter experiments, are time consuming in that they typically last for at least a few months and can last for up to three years. Lysimeter experiments are also costly to conduct. Because of restrictions such as these, relatively few deposits have been characterised to determine the leachate which they generate and thus the risk which they pose to the environment. There is an urgent need to be able to estimate the environmental risks associated with existing waste deposits. The first step towards assessing this risk would be an ability to predict leachate generation within a specific deposit. Such an ability could be used to identify which of the existing deposits produce significant leachate and thus pose a potential hazard to the environment. Equally, if leachate generation from new deposits could be estimated as a function of waste material and characteristics of the waste deposit, this information could be used to improve the engineering design of waste deposits. The work presented in this thesis involved identifying suitable modelling strategies which could be used to determine leachate generation within waste deposits which contain waste material typical of that produced by the minerals processing industry. Two modelling strategies have been investigated. The first modelling strategy involved a macroscopic model in which all effects such as intrinsic chemical kinetics, intra-particle diffusion, external mass transfer and hydrodynamic considerations are lumped into a single parameter. The result of this approach is an effective reaction rate for the release of hazardous constituents from a volume element of the waste deposit. The effective reaction rate is determined by fitting the model to experimental data based on lysimeter tests. The main advantage of this model is that it eliminates the need for a detailed understanding of the individual factors which contribute to leachate generation. This model was investigated both for its inherent simplicity and for use in cases where insufficient information with respect to the intrinsic chemical reaction rates, intra-particle diffusion, external mass transfer or hydrodynamic aspects exist. The main disadvantage of this model is that it has a limited predictive ability in that the individual significance of any one factor which contributes to leachate generation cannot be determined. For this reason a second, more detailed model, termed the heterogenous columnar model, has also been investigated. The heterogenous columnar model describes the release of hazardous constituents at the single particle level and relates this information to the overall leachate generation within the deposit. This is achieved by calculating the release of hazardous constituents from the size distribution of particles to the bulk fluid between these particles. The release of hazardous constituents from individual particles is determined by making use of a particle-scale chemical reaction 'model. This particle-scale model is sufficiently detailed to be able to determine the relative contribution to the overall release of hazardous constituents from the particles of intrinsic chemical kinetics of the reactions to the effects of diffusion of the fluid reagent into each particle. The heterogenous columnar model can also be used to determine whether the effective rate of release of hazardous constituents from the particles (which include intrinsic kinetic and diffusional contributions) or the flow of fluid reagent through the deposit limits the release of hazardous constituents from the deposit. This information can be used to determine the main factors which affect the release of hazardous constituents from waste deposits and can thus be used to improve the design of waste deposits. Probably the most important attribute of the heterogenous columnar model is that methods have been investigated to determine the model parameters from a simple continuously stirred tank reactor (CSTR) type experiment. The ability of the heterogenous columnar. model to predict leaching behaviour has been investigated using data on precious metal leaching found in the literature. The results are encouraging in that the model can accurately predict the leaching behaviour of precious metals. A preliminary investigation into determining suitable particle-scale model parameters for a sample of waste from a CSTR experiment has been conducted. This too has yielded encouraging results. However, the application of using the heterogenous columnar model using these parameters to describe leachate generation within waste deposits or lysimeter experiments still needs to be demonstrated. Once the heterogenous columnar model has been verified against data pertaining to leachate generation from a waste deposit it may start to provide the minerals processing industry with the information which it so desperately requires in order to dispose of wastes in a manner which minimises the impact on the environment.