The catalytic effect of potassium on the rate of CO₂ gasification of a bituminous coal char and a pure carbon substrate is investigated. The gasification rate depends on both the catalyst concentration (K/C atomic ratio) and the internal porous structure of the solid. For low values of the K/C atomic ratio, the initial gasification rate (mg carbon gasified per initial gram carbon per min) increases sharply with the addition of catalyst; at higher values, the rate profile levels off. The sharp increase in rate is due to the activation of reaction sites while the plateau is attributed to the saturation of the surface with active sites. The variation of the instantaneous gasification rate (based on remaining carbon) with carbon conversion at various initial K/C ratios is studied. The important reasons for the change in rate are the change in the solid surface area, the loss of active sites, the loss of catalyst by vaporization and the change in the K/C ratio due to carbon depletion. The loss of catalyst from the pure carbon substrate by vaporization is also determined. The extent of this loss depends primarily on the reaction start-up procedure. Temperature programmed experiments show that under inert atmospheres, both KOH and K₂CO₃ react with carbon to give a reduced form of the catalyst which appears to be a prerequisite for the rapid vaporization of potassium. The effect of catalyst loss on both the initial gasification rate and the variation in rate with conversion is determined. The reaction mechanism is studied by a temperature and concentration programmed reaction technique. The proposed redox mechanism contains three surface complexes: -CO₂K, -COK and -CK. The oxide groups are the intermediates during C/CO₂ gasification. The completely reduced form, -CK, is the end product of catalyst reduction and is the precursor for K loss. The stoichiometries of these surface groups are confirmed by oxygen and potassium balance.

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Submitted to: School of Mining Engineering, Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, South Africa September 2015 / Most coal seams in the Waterberg Coalfield contain medium to high levels of phosphorus in coal. Thermal coal, which has a lower value than metallurgical coal, is produced from these coal seams. Metallurgical coal used as feed for char production has especially stringent phosphorous content specifications. Phosphorous levels vary both laterally and vertically through the coal succession of the Vryheid Formation. If the coal horizons with elevated phosphorus could be identified and selectively removed, significant amounts coal could be saved and utilized as metallurgical coal through the life of the mine. Different mining horizons with regards to their phosphorus content have to be determined to increase the amount of char plant feed coal. Bench definitions and their techno-economic applications are therefore the main purpose of the current investigation. Bench 11 is currently the only source utilized for char plant feed coal. The char plant is therefore entirely dependent on coal supply from Bench 11. This poses a risk on the continual production of char at Grootegeluk Mine. It was determined that this bench is not suitable for char plant feed coal in certain areas of the resource. A high phosphorus coal horizon was identified in the upper portion of the bench. If this coal is removed separately, the phosphorus content of the coal in the remaining portion of the bench would be suitable for char plant feed coal. This alternative step is dependent on the phosphorus distribution in the resource and may therefore not always be effective. No changes to the other bench definitions could be established that would increase the amount of potential char plant feed coal. Three further aspects were investigated: The potential to reduce phosphorus in coal by means of coal beneficiation was determined. Results showed that phosphorus levels in coal cannot be lowered sufficiently by means of coal beneficiation. Secondly, the suitability of using different coal analyses to improve the estimation of phosphorus in coal was investigated. Results showed that phosphorus prediction and analyses cannot be enhanced nor replaced by other coal analyses. Lastly, the importance of Zone 1 as a source of low phosphorous coal was investigated. Zone 1 is currently not part of the mine plan, but if mined, it could be used as a source for blending; thereby increasing the amount of char plant feed coal from the reserves. In certain portions of the resource, utilizing Zone 1 may be the only feasible way of securing the continual supply of low phosphorus content coal. Analytical exploration borehole data of phosphorus in coal is limited in certain areas of the resource. Due to the variability of phosphorus in the coal horizons, more borehole data is required to increase the estimation accuracy of phosphorus in the coal. Based on such data, mining horizons might be changed in future to secure more char plant feed coal.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 246-250. / by Matthew Neville. / Sc.D.

Thesis. 1976. Ph.D.--Massachusetts Institute of Technology. Dept. of Mechanical Engineering. / Microfiche copy available in Archives and Engineering. / Vita. / Bibliography: leaves 414-423. / Ph.D.

A mathematical model for entrained flow coal gasification was developed with the objective of predicting the influence of coal properties and gasification conditions on the performance of entrained flow gasifiers operating at pressures up to 21 atmospheres (2.1MPa). The model represents gasifiers as plug flow reactors and therefore neglects any mixing or turbulence effects. Coal properties were predicted through use of correlations from a variety of literature sources and others that were developed from experimental data in the literature. A sensitivity analysis of the model indicated that errors in the calculated values of coal volatile yield, carbon dioxide gasification reactivity and steam gasification may significantly affect the model predictions. Similarly errors in the input values for gasifier wall temperatures and gasifier diameter, when affected by slagging, can cause model prediction errors. Model predictions were compared with experimental gasification results for a range of atmospheric and high pressure gasifiers, the majority of the results being obtained by CSIRO at atmospheric pressure for a range of coals. Predictions were accurate for the majority of atmospheric pressure results over a large range of gas feed mixtures. Due to the limited range of experimental data available for high pressure gasification the capability of the model is somewhat uncertain, although the model provided accurate predictions for the majority of the available results. The model was also used to predict the trends in particle reactions with gasification and the influence of pressure, gasifier diameter and feed coal on gasifier performance. Further research on coal volatile yields, gasification reactivities and gas properties at high temperatures and pressures was recommended to improve the accuracy of model inputs. Additional predictions and model accuracy improvements could be made by extending the model to include fluid dynamics and slag layer modelling. / PhD Doctorate

Thesis (M.S.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains viii, 72 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 46-48).

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