No description available.

Thesis (Ph. D.)--University of Sydney, 1987. / Includes tables. Bibliography: leaves 191-199. Also available in print form.

Thesis (M.S.)--University of Wisconsin--Madison, 1981. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 89).

Please read the abstract in the section 00front of this document / Dissertation (M Eng (Mechanical Engineering))--University of Pretoria, 2007. / Mechanical and Aeronautical Engineering / unrestricted

The high temperature interactions of alkali metal compounds with solids present in coal conversion processes are investigated. A temperature and concentration programmed reaction method is used to investigate the mechanism by which organically bound alkali is released from carbonaceous substrates. Vaporization of the alkali is preceded by reduction of oxygen-bearing groups during which CO is generated. A residual amount of alkali remains after complete reduction. This residual level is greater for potassium, indicating that potassium has stronger interactions with graphitic substrates than sodium. Other mineral substrates were exposed to high temperature alkali chloride vapors under both nitrogen and simulated flue gas atmospheres to investigate their potential application as sorbents for the removal of alkali from coal conversion flue gases. The compounds containing alumina and silica are found to readily adsorb alkali vapors and the minerals kaolinite, bauxite and emathlite are identified as promising alkali sorbents. The fundamentals of alkali adsorption on kaolinite, bauxite and emathlite are compared and analyzed both experimentally and through theoretical modeling. The experiments were performed in a microgravimetric reactor system; the sorbents were characterized before and after alkali adsorption using scanning Auger microscopy, X-ray diffraction analysis, mercury porosimetry and atomic emission spectrophotometry. The results show that the process is not a simple physical condensation, but a complex combination of several diffusion steps and reactions. There are some common features among these sorbents in their interactions with alkali vapors: In all cases the process is diffusion influenced, the rate of adsorption decreases with time and there is a final saturation limit. However, there are differences in reaction mechanisms leading to potentially different applications for each sorbent. Bauxite and kaolinite react with NaCl and water vapor to form nephelite and carnegieite and release HCl to the gas phase. However, emathlite reacts to form albite and HCl vapor. Albite has a melting point significantly lower than nephelite and carnegieite; therefore, emathlite is more suitable for lower temperature sorption systems downstream of the combustors/gasifiers, while kaolinite and bauxite are suitable as in-situ additives.

No description available.

Coal continues to be burned by direct combustion in packed or moving bed in small size domestic furnaces, medium size industrial furnaces, as well as small power stations. Recent stringent restrictions on exhaust emissions call for a better understanding of the process of combustion of coal in beds. The present study is a prelude to developing methods of analysis to obtain this improved understanding. A one-dimensional steady-state computational model for combustion of a bed of solid fuel particles with a counterflowing oxidant gas has been developed. Air, with or without preheating, is supplied at the bottom of the bed. Spherical solid fuel particles (composed of carbon and ash) are supplied at the top of the bed. Upon sufficient heating in their downward descent, the carbon in particles reacts with oxygen of the flowing gas. The governing equations of conservation of mass, energy, and species are integrated numerically to obtain the solid supply rate whose carbon content can be completely consumed by a given gas supply rate. The distributions of solid and gas temperatures, of concentrations of various gas species, of carbon content in solid, and of velocity and density of gas mixture are also calculated along the bed length. The dependence of these distributions on the solid and gas supply rates, the air supply temperature, the size of solid fuel particle, and the initial carbon content in solid is also investigated. The calculated distributions are compared with the available measurements from literature to find reasonable agreement. More gas supply is needed for complete combustion at higher solid supply rate. At a given gas supply rate, more solid fuel particles can be consumed at higher gas supply temperature, for larger particle size, and for lower initial carbon content in solid. The temperature of the bed becomes higher for higher solid supply rate, higher gas supply temperature, larger solid particle diameter, or lower initial carbon content in solid. These reasonable results lead one to encourage extension of the model presented here to more complex problems involving combustion of coals in beds including the effects of drying and pyrolysis. / Graduation date: 1994

No description available.

One or the characteristics of all anthracite coal, with its low volatile content, is its ability to burn completely in a small volume. Another characteristic and disadvantage of local, semi-anthracite coal is its high ash content. It is the authors' belief that local, semi-anthracite coal can be burned most effectively for domestic heating if the furnace design allows for these characteristics. With these facts in mind, it was decided that the Anthratube had excellent possibilities as a domestic unit for burning local coal. The Anthratube, by its compactness, takes full advantage of the first characteristic; with its ash-removing grate, it overcomes to a great extent the disadvantage of the second characteristic. The purpose of this thesis was, then, to determine whether or not various sizes of local, semi-anthracite coal from the Merrimac seam could be successfully burned in the Anthratube. The coal used for this investigation was obtained from the Great Valley Anthracite Corporation located at McCoy, Virginia. 1. Pea size, local coal can be burned very successfully in the Anthratube. Overall boiler efficiencies of the unit with this size coal are high over a wide range of loads. Of the sizes of coal burned, pea size is most suitable for the Anthratube. 2. Buckwheat size, local coal canoe burned in the Anthratube with good results. The overall boiler efficiencies obtained with this size of coal are good, although not as high as those obtained with the pea coal. 3. The performance of the Anthratube with rice size, local coal is inferior to that achieved with pea and buckwheat sizes. The output of the unit is seriously limited when using this size. 4. Culm size, local coal cannot be burned in the Anthratube. / M.S.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master in Science in Engineering, Johannesburg September 1998 / Combustion modelling of utility furnace chambers provides a cost efficient means to extrapolate the combustion behaviour of pulverised fuel (pf) as determined from drop tube furnace (DTF) experiments to full scale plant by making use of computational fluid dynamics (CFD). The combustion model will be used to assimilate essential information for the evaluation and prediction of the effect of • changing coal feedstocks • proposed operational changes • boiler modifications. TRI comrnlssloned a DTF in 1989 which has to date been primarily used for the comparative characterisation of coals in terms of combustion behaviour. An analysis of the DTF results allows the determination of certain combustion parameters used to define a mathematical model describing the rate at which the combustion reaction takes place. This model has been incorporated into a reactor model which can simulate the processes occurring in the furnace region of a boiler, thereby allowing the extrapolation of the DTF determined combustion assessment to the full scale. This provides information about combustion conditions in the boiler which in turn are used in the evaluation of the furnace performance. Extensive furnace testwork of one of Eskom's wall fired plant (Hendrina Unit 9) during 1996, intended to validate the model for the ar plications outlined above, included the measurement {If : • gas temperatures • O2, C02, CO, NOx and S02 concentrations • residence time distributions • combustible matter in combustion residues extracted from the furnace • furnace heat fluxes. The coal used during the tests was sampled and subjected to a series of chemical and other lab-scale analyses to determine the following: • physical properties • composition • devolatilisation properties " combustion properties The same furnace was modelled using the University of Stuttgart's AIOLOS combustion code, the results of Which are compared with the measured data. A DTF derived combustion assessment of a coal sampled from the same site but from a different part of the beneficiation plant, which was found to burn differently, was subsequently used in a further simulation to assess the sensitivity of the model to char combustion rate data. The results of these predictions are compared to the predictions of the validation simulation. It was found that the model produces results that compare well with the measured data. Furthermore. the model was found to be sufficiently sensitive to reactivity parameters of the coal. The model has thereby demonstrated that it can be used in the envisaged application of extrapolating DTF reactivity assessments to full scale plant. In using the model, it has become apparent that the evaluations of furnace modifications and assessments of boiler operation lie well within the capabilities of the model. / MT2017