Study of Methane Outgassing and Mitigation in Longwall Coal Mines
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Study of Methane Outgassing and Mitigation in Longwall Coal Mines Samuel A. Lolon 1
&
Jürgen F. Brune 2 & Gregory E. Bogin Jr 3 & Aditya Juganda 2
Received: 5 June 2020 / Accepted: 11 August 2020 / Published online: 24 August 2020 # Society for Mining, Metallurgy & Exploration Inc. 2020
Abstract Historically, there have been many occurrences of mine fires and explosions recorded in the United States and other countries that have demonstrated the existence of explosive methane–air mixtures, herein referred to as explosive gas zones (EGZs). The risk of mine explosions can increase if the EGZs migrate out from the gob into the surrounding mine entries. Fluctuating barometric pressure is the common cause for EGZs outflowing or outgassing from the gob. Numerical analysis using a 3D computational fluid dynamics method was developed to fully understand the outgassing phenomenon. A number of simulations using various magnitudes and periods of barometric pressure changes indicated that the EGZ outgassing potentially occurs due to lags in pressure, which are strongly influenced by mine conditions and ventilation systems. An early warning system with a real-time pressure monitoring and the application of gob ventilation boreholes are recommended to detect and mitigate explosion hazards from gob outgassing. Keywords Gob outgassing . Barometric pressure variation . Computational fluid dynamics (CFD) . Explosive gas zone (EGZ) . Methane gas
1 Introduction In underground longwall coal mining, the mined-out areas or gobs frequently contain methane, which can form explosive methane–air mixtures. Historically, there have been many occurrences of mine fires and explosions recorded in the United States and other countries that have demonstrated the existence of such explosive mixtures, herein referred to as explosive gas zones (EGZs), inside and around the perimeter of bleeder-ventilated longwall gobs [1–6]. The risk of mine
* Samuel A. Lolon [email protected] Jürgen F. Brune [email protected] Gregory E. Bogin, Jr [email protected]
explosions can increase if the EGZs migrate out from the gob into the surrounding mine entries. Several factors can induce EGZs outflowing from the gob, but the common cause is the fluctuating barometric pressure as it naturally occurs every day. This atmospheric pressure change can fluctuate abruptly and become increasingly hazardous in adverse weather conditions. Other sudden pressure changes can result from roof falls, failing ventilation controls, and fan outages. Any such fluctuation of mine ventilation pressure may disturb the pressure differential between the gob and the surrounding mine workings and may cause EGZs to outgas from the gob. The correlation between major mine explosions and abrupt barometric pressure changes has been studied and confirmed for explosions in coal mining countries, including the United States, South Africa, Australia, and Poland [7–14]. Disastrous mine explosions appear to happen more frequently during stormy weather, which, in the United States, typically occurs durin
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