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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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 (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

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