Gases evolved and possible reactions during low-temperature oxidation of coal

Preliminary experiments have been made by pace-heating three coals from about −40 °C to 120 °C at a rate of 0.5 °C/min in various concentrations of oxygen and analysing the effluent gases. Carbon monoxide was always the predominant gas produced. At the lower temperatures its production appeared to be more dependent on temperature than on atmospheric oxygen content. However, there is evidence of a critical temperature — about 70 °C — above which, provided that sufficient oxygen is available, spontaneous combustion of coal becomes inevitable. If the exothermic reactions could be controlled to prevent coal exceeding the critical temperature, incipient heating might be prevented. Even below 70 °C traces of certain gases were formed, some doubtless components of ‘gobstink’, the smell characteristic of spontaneous combustion, but in quantities too small to be reliably measured. Chemical mechanisms are suggested and tested in part, and determinations of carbon monoxide and acetaldehyde concentrations in a working colliery have provided some confirmation of them.