Identification of low temperature combustion products from coal and a study of their effect on metal oxide semiconductors

Gibson, S., 1988. Identification of low temperature combustion products from coal and a study of their effect on metal oxide semiconductors. PhD, Nottingham Trent University.

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A large number of the gaseous products evolved from coal heated in the laboratory have been identified using a wide range of analytical procedures. Typical first appearance temperatures and concentration versus temperature profiles of the products were established under well defined experimental conditions in air and nitrogen. Three distinct patterns of evolution were observed and several products not previously considered to be present in the temperature range studied were identified. Carbon monoxide is currently used to indicate the onset of spontaneous combustion of coal. A number of other products were identified which appeared to have potential as alternative indicators including unsaturated hydrocarbons, benzene and toluene, methylcyclohexene, Sulphur containing compounds, carbonyl species, hydrogen chloride and hydrogen.

The presence underground of many of these products was confirmed and their evolution patterns in relation to carbon monoxide during incidents of spontaneous combustion were studied in detail. Whilst carbonyl sulphide appeared to be the only definitive indicator of spontaneous combustion it was demonstrated that the ratio of different products to carbon monoxide may reveal a greater understanding of the degree and extent of activity of an incident of spontaneous combustion. The presence of methane in association with low aliphatic hydrocarbons underground was largely unaffected during the development of incidents of spontaneous combustion, any variations being due to a greater extent to other factors.

Three commercially available tin oxide based semiconductor gas sensors, namely, the TGS 711, 812 and 813 were selected for the detection of the products evolved from heated coal. The type 711 and 812 gas sensors were investigated for the detection of spontaneous combustion and the type 813 sensor for the measurement of methane concentrations. The basic operating characteristics of the sensors were investigated, including composition, surface morphology, working temperature, ambient atmosphere dependence and effect of varying oxygen concentration. It was demonstrated that if measurements were performed under well defined operating conditions the sensors exhibited consistent behavior.

The effect of the products evolved from heated coal, both as individual species and collectively on the response of the gas sensors was investigated. This approach made it possible to identify the range of products which made significant contributions to the total sensor responses. Whilst the sensors lacked sufficient selectivity to be used as specific gas detectors, it was demonstrated that for the detection of spontaneous combustion the type 711 and 812 sensors have the potential to form the basis of a highly sensitive practical underground monitoring system indicating the presence of the products evolved during the low temperature heating of coal. However, the response characteristics of the 813 sensor were less amenable to the design of a single instrument for the direct measurement of methane concentrations.

Item Type: Thesis
Creators: Gibson, S.
Date: 1988
ISBN: 9781369325126
Rights: This copy of the thesis has bean supplied on condition that anyone who consults it is understood to recognise that its copyright rests with its author and that no quotation from the thesis and no information derived from it may be published without the author's prior written consent
Divisions: Schools > School of Science and Technology
Record created by: Laura Ward
Date Added: 25 Jun 2021 13:37
Last Modified: 01 Nov 2023 15:29

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