Analysis of the Consequences of Methane Combustion in a Mined Dog Heading

Abstract

One of the most common and, at the same time, the most serious threats in underground hard coal mining, which often requires long rescue operations, is the methane hazard. It is related to the potential ignition and/or explosion of methane in mixture with air. The hazard grows along with the increasing depth of mining works and the concentration of production in mine headings. Methane, as an organic gas, is released to the mining atmosphere in the exposed body of coal. Accumulation of explosive concentrations of methane in a mine heading, as well as adequate oxygen concentration levels and the presence of a trigger (e.g. in the form of a spark) may lead to methane explosion or combustion. Methane ignition and combustion leads to a series of chemical reactions, which cause the emission of harmful and poisonous gases of high temperature into the mining atmosphere (the temperature of methane combustion in mixture with air is approx. 1,875°C, with methane content of approx. 10%). These gases are formed during methane combustion. Countering the methane hazard primarily involves elimination of the potential for dangerous methane concentration levels and application of suitable protective measures to prevent methane ignition. However, despite the preventive measures in use, there were 34 incidents related to the methane hazard in Polish hard coal mines in the years 2008–2018, including 10 cases of methane ignition in the mined dog headings. Therefore, it is necessary to carry out research in order to predict the consequences caused by methane combustion in mine headings. Taking into consideration the remarks above, it was assumed that the numerical analysis of methane combustion in the mined dog heading and of the impact of this combustion on the parameters of the air stream flowing through this heading would be conducted using the CFD method. The objective of the analysis was to determine the effects of methane combustion on the composition of the mining atmosphere and the physical parameters of the gas mixture generated in this process. The paper presents the distributions for the physical parameters of the resulting gas mixture and the concentration of fire gases. Moreover, it demonstrates the distributions for temperature and oxygen concentration levels in the heading under analysis.