Analysis of adsorption tests of gases emitted in the coal self-heating process

• Sorption measurements of CO, CO2, H2, C2H4, C3H6, and C2H2 were conducted on hard coals.
• Low-rank coals of high oxygen content and porosity sorb the largest amounts of gases.
• Process of sorption may cause a decrease in concentration of those gases in mine air.
• Fire indices should be constructed based on gases of similar sorbability.

The analysis of the results of sorption absorbency of hard coals with respect to gases relevant in assessing the fire hazard (carbon monoxide, carbon dioxide, hydrogen, ethylene, propylene, and acetylene) was the aim of this study. Hard coals adsorb carbon dioxide and acetylene in the highest amount, and ethylene and propylene in a slightly smaller amount. The adsorption of carbon monoxide and hydrogen is very small. The amounts of adsorbed gases depend on the metamorphism degree of hard coals as well as on their porosity. Hard coals of high porosity with good accessibility of internal surface, of low metamorphism degree and of higher oxygen content are characterized by greater adsorption capacity. Fire gases generated from the self-heating center may be the subject to adsorption on hard coals, which results in the lower gas concentration at the measuring points and as a consequence in the change of fire indicators calculated on their basis. This phenomenon applies in particular to hard coals with high sorption absorbency and to the situation in which the self-heating center and the point of measurement of concentrations is considerably distant, which causes greater contact of the emitted gas with coal matter, and more possible intensification of the adsorption process.Fire indicators are used to assess the development of the process of self-heating of coal. Gases, the concentration of which is the part of the particular fire indicator, should have a similar adsorption capacity. Indicators constructed on the basis of a very different adsorption capacity can be a source of errors due to the observed adsorption process.