The purpose of this interdisciplinary thesis is to relate the scientifically known environmental effects of the coal- and oil-fired electricity generation fuel cycles in the UK to the economic, legal and political considerations which bear upon energy/environment analyses. Where possible the, environmental effects of the two fuel cycles are compared. Throughout differences with other countries, particularly the US, in both the perceived environmental effects and prescriptions for dealing with them are highlighted. It is shown that although where the environmental effects can be evaluated the coal fuel cycle tends to have a more adverse impact than the oil cycle, these effects are so small in economic terms that no clear fuel policy implications emerge. Indeed fuel policy in the past has been little influenced by environmental considerations. Moreover the law relating to pollution in the UK, based on the principle of "best practicable means", generally operates more efficiently than the less flexible systems of other countries and successfully implements the prescriptions of economic theory to internalise externalities and make the polluter pay. However, the vast majority of the effects of the oil and coal fuel cycles cannot be quantified, in economic terms, either because they are not understood scientifically, or because they are of an essentially subjective nature. This renders much of the (sometimes elaborate) economic theory of how best to internalise externalities largely redundant since the optimal position towards which it aspires can seldom be identified. For the same reason, the usefulness of energy/environment models which purport to display the environmental consequences of different energy balances is also restricted. Moreover, an understanding of the complicated and seldom linear relationships that usually exist between the effect of a pollutant and level of energy output exposes the difficulties and dangers of formulating the normalised environmental impact indices which are the ultimate objective of many energy/environment models.

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A semi-batch Direct Coal Liquefaction facility was designed and constructed in order to examine the impact of process variables on coal liquefaction kinetics. A series of parametric investigations involving bituminous, sub-bituminous coals and lignite were performed. The process variables included solvent composition, catalyst to coal ratio, the intensity of turbulence, the initial dissolved hydrogen concentration, and the slurry residence time distribution. The results of these investigations showed that process variables have a significant impact on the rates of liquefaction reactions, and that reaction rates for coal and lignite are affected in a similar manner. The overall rate and maximum extent of liquid and gas production was found to depend on the initial rate of molecular hydrogen transfer to the coal particles, and on the ratio of the intensity of turbulence to the level of catalysis. This latter finding led to the discovery of a persistent dispersed liquid phase within the coal liquefaction environment. A reaction model, coupling these findings with a simple kinetic scheme, was found to correlate the liquefaction behaviour of bituminous and sub-bituminous coals and lignite, in diverse reaction environments. The experimental results and the reaction model were used to develop novel design criteria for Direct Coal Liquefaction Reactors. Two design optima were identified. One optimum is closely approximated by an existing process. An alternative and potentially preferable optimum is proposed. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

The relative floatability of coal and other inherently hydrophobic solids in aqueous solutions of short-chain n-alcohols was studied. An analysis of wettability data from the literature for such systems indicated that, in general, a linear relationship existed between the solution surface tension, Y1v» and the adhesion tension, Y1v COS Ɵ (where Ɵ is the contact angle). Except for very non-polar solids, the critical surface tension of wetting, Yc (Ɵ= 0° intercept), determined with the alcohol solutions, was relatively constant and independent of the type of solid. The parameter which reflected the relative wettability of a solid was the slope of its Y1v cos Ɵ vs. Y1v line. Since wettability and floatability are not necessarily synonymous, a concept of critical surface tension of floatability, Ycf, was developed to characterize the threshold floatability condition where successful bubble-particle attachment was controlled by either adhesion or aggregate stability. In both cases it was concluded that Ycf would depend on the surface and the physical properties of a particle for a given set of flotation conditions, and that Ycf > Yc . Under certain circumstances it also appeared that selective flotation separation between particles of two inherently hydrophobic solids, A and B, would be feasible in an aqueous alcohol solution if Ycf A < Y1v ≤ Ycf B even when the two solids had the same Yc value. Small-scale flotation tests in aqueous methanol solutions were performed on narrow size fractions of several inherently hydrophobic solids. In most cases the wt.% floated decreased from a maximum to a minimum over a discrete range of Y1v, implying that the particles in a sample had a range of Ycf values. The relative floatability of a sample was given by the position of its Ycf band along the Y1v axis. For the same size fraction, floatability decreased in the order: polytetrafluoroethylene (PTFE), sulphur, medium volatile bituminous coal, molybdenite. Almost complete selective separation by flotation was achieved between samples whose Ycf bands did not overlap. Because coal is a very heterogeneous material, it was expected that a sample of fine coal particles would display a wide range of wettability and floatability characteristics, with a corresponding broad range of Ycf values. This was verified in aqueous methanol solutions for narrow particle size fractions of several high rank coal samples from the East Kootenay coalfield, British Columbia. Incremental ash content/floatability relationships were developed which could be roughly divided into two main regions'. In one, the coal particle ash content was low and independent of floatability, while in the other they were inversely related. The effects of physical and compositional factors other than ash content on the distribution of floatability within a coal sample have been discussed. For a readily floatable coal sample the yield-ash content relationships for the flotation products were independent of the flotation time and conditioning time, and were considered to approximate the ideal flotation wash-ability characteristics of the sample. Flotation washability was found to be linearly related to feed ash content. The shape and position of the incremental ash content/floatability curves for different coal samples allowed the relative wettabilities of their organic matter to be assessed in terms of degree of oxidation, rank and petro-graphic composition. Coal sample floatability in aqueous methanol solutions was found to be sensitive to small differences in surface properties which were not reflected by bulk compositional parameters. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

In modern coal preparation plants, solid-solid and solid-liquid separation processes used to treat fine coal are least efficient and most costly operations. For example, field studies indicate that the froth flotation process, which is normally used to treat minus (-0.2 mm) fine coal, often recovers less than 65 to 70% of the organic matter in this size range. Fine coal separation processes are also inherently less effective in removing pyrite than that of coarse coal separations. Moreover, while fines may represent 10% or less of the total run-of-mine feed, this size fraction often contains one-third or more of the total moisture in the delivered product. In order to address these issues, several multistage coal processing circuits were set up and experimentally tested to demonstrate the potential improvements in fine coal upgrading that may be realistically achievable using an "optimized" fine coal processing flowsheet. On the basis of results obtained from this research, engineering criteria was also developed that may be used to identify optimum circuit configurations for the processing different fine coal streams. In the current study, several fine coal cleaning alternatives were evaluated in laboratory, bench-scale and pilot-scale test programs. Fine coal processes compared in the first phase of this work included spirals, water-only cyclones, teeter-bed separators and froth flotation. The performance of each technology was compared based on separation efficiencies derived from combustible rejection versus ash rejection plots. The resulting data was used to identify size ranges most appropriate for the various alternative processes. As a follow-up to this effort, a second phase of pilot-scale and in-plant testing was conducted to identify new types of spiral circuit configurations that improve fine coal separations. The experimental data from this effort indicates that a four-stage spiral with second- and fourth-stage middlings recycle offered the best option for improved separation efficiency, clean coal yield and combustible recovery. The newly developed spiral circuitry was capable of increasing cumulative clean coal yield by 1.9 % at the same clean coal ash as compared to that of achieved using existing conventional compound spiral technology. Moreover, the experimental results also proved that slurry repluping after two turns is not effective in improving separation performance of spiral circuits. The third phase of work conducted in this study focused on the development of methods for improving the partitioning of pyrite within fine coal circuits. The investigation, which included both laboratory and pilot-scale test programs, indicated that density-based separations are generally effective in reducing sulfur due to the large density difference between pyrite and coal. On the other hand, the data also showed that sulfur rejections obtained in froth flotation are often poor due to the natural floatability of pyrite. Unfortunately, engineering analyses showed that pyrite removal from the flotation feed using density separators would be impractical due to the large volumetric flow of slurry that would need to be treated. On the other hand, further analyses indicated that the preferential partitioning of pyrite to the underflow streams of classifying cyclones and fine wire sieves could be exploited to concentrate pyrite into low-volume secondary streams that could be treated in a cost effective manner to remove pyrite prior to flotation. Therefore, on the basis of results obtained from this experimental study, a combined flotation-spiral circuitry was developed for enhanced ash and sulfur rejections from fine coal circuits. Finally, the fourth phase of work conducted as part of this investigation focused on evaluating a new mechanical, non-thermal dewatering process called Nano Drying Technology (NDT"). Experimental results obtained from bench-scale testing showed that the NDT" system can effectively dewater fine clean coal products from more than 30% surface moisture to single-digit moisture values. Test data obtained using a pilot-scale NDT" plant further validated this capability using a continuous prototype facility. It was also observed that, unlike existing fine coal dewatering processes, the performance of the NDT" system is not constrained by particle size. / Ph. D.

In modern coal preparation plants, solid-solid and solid-liquid separation processes used to treat fine coal are least efficient and most costly operations. For example, field studies indicate that the froth flotation process, which is normally used to treat minus (-0.2 mm) fine coal, often recovers less than 65 to 70% of the organic matter in this size range. Fine coal separation processes are also inherently less effective in removing pyrite than that of coarse coal separations. Moreover, while fines may represent 10% or less of the total run-of-mine feed, this size fraction often contains one-third or more of the total moisture in the delivered product. In order to address these issues, several multistage coal processing circuits were set up and experimentally tested to demonstrate the potential improvements in fine coal upgrading that may be realistically achievable using an "optimized" fine coal processing flowsheet. On the basis of results obtained from this research, engineering criteria was also developed that may be used to identify optimum circuit configurations for the processing different fine coal streams. In the current study, several fine coal cleaning alternatives were evaluated in laboratory, bench-scale and pilot-scale test programs. Fine coal processes compared in the first phase of this work included spirals, water-only cyclones, teeter-bed separators and froth flotation. The performance of each technology was compared based on separation efficiencies derived from combustible rejection versus ash rejection plots. The resulting data was used to identify size ranges most appropriate for the various alternative processes. As a follow-up to this effort, a second phase of pilot-scale and in-plant testing was conducted to identify new types of spiral circuit configurations that improve fine coal separations. The experimental data from this effort indicates that a four-stage spiral with second- and fourth-stage middlings recycle offered the best option for improved separation efficiency, clean coal yield and combustible recovery. The newly developed spiral circuitry was capable of increasing cumulative clean coal yield by 1.9% at the same clean coal ash as compared to that of achieved using existing conventional compound spiral technology. Moreover, the experimental results also proved that slurry repluping after two turns is not effective in improving separation performance of spiral circuits. The third phase of work conducted in this study focused on the development of methods for improving the partitioning of pyrite within fine coal circuits. The investigation, which included both laboratory and pilot-scale test programs, indicated that density-based separations are generally effective in reducing sulfur due to the large density difference between pyrite and coal. On the other hand, the data also showed that sulfur rejections obtained in froth flotation are often poor due to the natural floatability of pyrite. Unfortunately, engineering analyses showed that pyrite removal from the flotation feed using density separators would be impractical due to the large volumetric flow of slurry that would need to be treated. On the other hand, further analyses indicated that the preferential partitioning of pyrite to the underflow streams of classifying cyclones and fine wire sieves could be exploited to concentrate pyrite into low-volume secondary streams that could be treated in a cost effective manner to remove pyrite prior to flotation. Therefore, on the basis of results obtained from this experimental study, a combined flotation-spiral circuitry was developed for enhanced ash and sulfur rejections from fine coal circuits. Finally, the fourth phase of work conducted as part of this investigation focused on evaluating a new mechanical, non-thermal dewatering process called Nano Drying Technology (NDT™). Experimental results obtained from bench-scale testing showed that the NDT™ system can effectively dewater fine clean coal products from more than 30% surface moisture to single-digit moisture values. Test data obtained using a pilot-scale NDT™ plant further validated this capability using a continuous prototype facility. It was also observed that, unlike existing fine coal dewatering processes, the performance of the NDT™ system is not constrained by particle size. / Ph. D.

A general review of the literature pertaining to the combustion of coal in an atmospheric fluidized bed of ,inert particles is presented. In particular, the phenomena of fluidization and combustion have been investigated and the status of research and development in various parts of the world is considered. A 300 mm diameter refractory lined open top atmospheric fluidized bed combustor has been built to study the combustion efficiencies and entrainment rates of the fluidized-bed combustion process in shallow fluidized beds, with static bed heights ranging from about ISO mm to 23J mm. A low pressure drop the of distributed was used for all of the tests so as to test a system compatible with most industrial requirements. As the combustor vessel is refractory lined, cooling is provided by supplying air to the rig well in excess of that required for stoichiometric combustion. As a result, no oxygen deficient regions occur within the fluidized bed, ensuring complete combustion of both the fixed carbon component of the coal to carbon dioxide and the volatile component within the bed section. Experimental results have been obtained from the combustion of a coal with a high fines content of which there is at present a supply which exceeds the demand. The coal has been burned in an inert bed comprising a closely graded silica sand. It has been found possible to correlate the combustion efficiencies in terms of the bed temperature, superficial gas velocity and the static bed height within the following ranges of these parameters: Bed Temperature Gas Velocity Static Bed Height 700 to 10000C 0,9 to 1,5 m/s 150 to 230 mm by using a bed material substantially different from the coal feed, it has been found possible to separate the (i) ABSTRACT A

M.Phil. / Coal forms an important role in the energy balance of the world economy. Despite having lost market share to gas in recent years, due to its vast reserves coal will continue to play a massive role in future energy markets. Up to now numerous studies have been completed on the major coal producing countries including South Africa, Australia and the United States. However no in-depth study of the smaller coal producing countries in Africa has been done. This dissertation would first identify the coal producing countries in Africa, estimate the possible reserves of each country and with the use of maps show the location of these reserves. Thereafter this dissertation will evaluate the infrastructure of the different coal producing countries to determine the possible coal export opportunities that exist in these countries. Factors influencing these export opportunities will also be investigated. The study will include South Africa but it will in no way be the focal point. A study of this nature will be extremely informative giving conclusions to the potential coal reserves that exist throughout Africa and will identify the possible export potential of this region.