Analysis of methane emission into the atmosphere as a result of mining activity

One of the most dangerous greenhouse gases that cause intensification of greenhouse effect is methane. It is odorless, lighter than air, colorless gas of organic origin, which is a highly energetic fuel. At the concentration in air within 5% to 15%, methane becomes an explosive gas and thus it is very dangerous. One of the main places of its occurrence are underground deposits of hard coal, where it is a serious danger for the process of their exploitation. In the coal deposits methane occurs in two fundamental forms as adsorbed methane, physical-chemically bounded with coal substance and as free methane, present in the pores and slits of pyrolytic rocks and coal. Methane confined it the pores as the result of coal mining is emitted into the mine atmosphere and further using ventilation ducts is released at the surface to the natural environment. Amount of emitted methane from one ton of mined coal is determined as its methane content, which in Polish mines is very high. It can be assumed that in Poland hard coal mines are the biggest source of this gas. In 2014 as a result of the mining activity approximately 570.11 million m³ of this gas were released to the atmosphere. Every day, taking into account the number of exploited longwalls, 14462.46 m³ of methane was transferred into the atmosphere, which gives the ventilation methane content of the level of 10.4 m³/min per longwall. In the paper, basing on the results of numerical analysis there was presented mechanism of release of methane from mined rock mass and rockfall goaves from mine headings and further through the ventilation system to the surface into the atmosphere. Also the amount of methane released into the atmosphere was estimated, illustrated by an example of one of the exploitation longwall. Also the most often ways used for decreasing amount of methane released into natural environment were discussed. Obtained results are very significant during taking the preventive actions in order to limit methane emission to external environment in the methane drainage process.