Thesis (doctoral)--Universiteit van Amsterdam. / Summary in Dutch. Includes bibliographical references.

Bibliography: leaves 234-252. The devolution times of seven coals were determined by measuring the centre temperature response for single particles held stationary in a bench scale atmospheric fluidised-bed reactor.

Kinetics of steam gasification of both delayed and fluid cokes, byproducts from thermal cracking processes of Athabasca bitumen, have been studied in laboratory-size stirred and fixed bed reactors. The hydrogen sulphide in the product gas was captured in-situ using calcined dolomite and limestones as acceptors. Experiments were carried out at atmospheric pressure and at temperatures between 800°C and 930°C. The coke particle size ranged from 0.1 to 3.5 mm, and the steam partial pressure was varied from 15.15 to 60.6 kPa. The carbon and sulphur conversions were computed from the knowledge of gas compositions and flowrates and the gasification kinetics of both species established. The effects of sorbent type, particle size, calcination conditions, and Ca/S molar ratios on the extent of sulphur capture during gasification were examined in separate series of experiments. Scanning electron microscopy, surface area analysis, and mercury porosimetry were employed to relate physical structure changes in the solids to experimental kinetic data. The rate of gasification for the delayed coke was generally higher than that for the fluid coke, and both cokes were almost unreactive to steam gasification at temperatures below 800°C. Increased reaction temperatures or reduced particle sizes increased both carbon as well as sulphur conversion. The carbon conversion rates were found to go through maxima as the time of reaction and extent of conversion increased. As the reaction proceeded the surface area of the coke increased to a maximum of about five times its initial value and thenfell off sharply. The extent of carbon conversion alone dictated the specific surface area irrespective of temperature, particle size and steam partial pressure. Both calcined dolomite and calcined limestone were found to be effective in removing sulphur from the product gas. Sorbents possessing a larger specific area or smaller grain size had higher capacity to accept sulphur. At a Ca/S molar ratio of 2.0, the overall sulphur removal was approximately 90% for the first 3 hrs and the H₂S concentration in the produced gas was reduced to about 200 ppm from nearly 1250 ppm. The rate of sorbent conversion from CaO to CaS decreased monotonically with time. Three available kinetic models for gasification - the Random Capillary Model, the Random Pore Model and the Modified Volumetric Model, were tested with the experimental gasification data. Although reasonable fits were obtained for Xc-t results, the sharp drop in rate at high conversion could not be adequately modelled. Rate constants were established for the initial stage of reaction only. The Grain model and Continuous reaction models were tested with the experimental sulphidation results. The sulphidation process was controlled by chemical reaction at low sorbent conversion, and subsequently by diffusion through the product layer at higher conversions. The reaction rate constant and the effective diffusivity were accordingly established as functions of temperature. Values compared favourably with results of sulphidation kinetics done without simultaneous gasification reported in the literature. The results suggest that the gasification process and the sulphur capture process, which occur together in gasifiers with sorbent injection, can be treated independently. Indexing terms: Gasification, Carbon Conversion, Sulphur Conversion, Sulphur Removal, Calcine, Limestone, Dolomite, Hydrogen Sulphide, Sulphidation. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Three different Western Canadian coals were gasified with air and steam in a fluidized bed of 0.73 mm Ottawa sand and coal, at atmospheric pressure, and temperatures of 1023 - 1175 K to produce a low Btu gas. The coals tested were of two types: one non-caking and two caking coals. The results were compared with those previously obtained for the same three coals when gasified in essentially the same equipment, but operated as a spouted bed. The effects of temperature, coal feed rate, air to coal ratio, steam to coal ratio, coal quality, coal particle size, and bed depth on the gas composition, gas calorific value and the operating stability of the gasifier, were established by running gasification tests over a wide range of operating conditions. Typical calorific value of the gas obtained for all three coals was in the range of 2.0 - 2.6 MJ/m³, which is lower than reported for the spouted bed and commercially available fluidized bed gasifiers. Analysis of the results suggested that in the present low temperature gasifier, the combustion and pyrolysis reactions predominate over the gasification reactions. The ability to treat caking coals in fluidized bed and spouted bed reactors is discussed. It is concluded that the dispersion of coal in a bed of inert silica and ash, rather than hydrodynamic characteristics is the key-factor in their success in handling caking coals. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Unknown

No description available.

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Call number: LD2668 .T4 1979 H69 / Master of Science

No description available.

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering Johannesburg, 29 August 2016 / This study discusses underground coal gasification (UCG) and the analysis thereof. Two main methods were used. The first is the Bond Equivalent Diagram, which gives an ideal of where operations should take place in relation to their coal and product gas compositions. This method was used to analyze several real life sites for their idealized and actual operations. The second consisted of a comparative exergy simulation study. This was done for an air-blown UCG plant with a downstream Fischer-Tropsch reactor and an oxygen-blown UCG plant with upstream air separation. The plants were analyzed by their overall exergy efficiency as well as their exergy outputs with respect to coal inputs (fuel). It was discovered that the air-blown simulation with downstream Fischer-Tropsch was the better choice from an exergy point of view due to it having higher efficiencies (1.5 for overall, 1.38 for fuel) as opposed to the oxygen-blown simulation (0.77 overall, 0.8 for fuel). This coupled with other design and safety factors led to the conclusion that the air-blown simulation was better. / MT2017

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