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Forecast of methane emission from closed underground coal mines exploited by longwall mining - a case study of Anna coal mine

Duda A., Krzemień A.

Journal of Sustainable Mining

2018

Vol. 17, iss. 4

184--194

Closure and post-closure periods in underground coal mines present specific risks that have to be handled with sound management practices in order to achieve sustainability within the mining sector. These risks may negatively affect the environment and result in hazards on the surface caused by phenomena occurring in the rock mass after mining operations. One of the hazards that has to be considered in the process of coal mine closure is gas, which is caused by methane emission after mining operations cease. This paper presents a forecast of methane emissions conducted within the framework of the Research Fund for Coal and Steel “MERIDA” project, using a model that was developed by the National Institute for the Environment and Industrial Hazards (INERIS) from France, and the Central Mining Institute (GIG) in Katowice, from Poland. This model enables the estimation of the volume of methane emitted into longwall goafs from relaxed undermined and overmined coal seams in order to assess in a further step the risk of methane emissions into the atmosphere from closed/sealed underground coal mines. For a critical analysis of the forecasted methane emissions into the longwall goafs, the results obtained with this model were compared with a gas decline curve generated for longwall goafs from closed/sealed underground coal mines in Australia, where long term full range data was available. The results of the analysis allowed the forecasted emissions and, thus, the accuracy of the model to be validated. The forecast was developed in the “Anna” coal mine, property of the PGG Company, which is located in the southern part of the Upper Silesian region in the south of Poland, near the border with the Czech Republic, and that is undergoing a closure process.

The use of a unipore diffusion model to describe the kinetics of methane release from coal spoil in the longwall environment

Wierzbicki M., Skoczylas N., Kudasik M.

Studia Geotechnica et Mechanica

2017

Vol. 39, nr 2

81--89

The unipore methane diffusion model based on the solution of the second Fick’s law describes effectively the kinetics of methane release from coal grains. The knowledge of the model describing the kinetics of methane release from coal, the coalbed methane content, the sorption isotherm, the effective diffusion coefficient and the coal particle size distribution, enables the calculation of the volume of methane which is released from the coal spoil as a function of time. These assumptions became the basis for building the software that enables the analysis of methane emissions from coal during the longwall mining. Simulations were performed to determine the temporal and spatial methane inflow to the longwall. The share of methane emission from coal grains (taking into account both the emission kinetics and mass participation) of various classes has been analyzed. The results of the analysis showed that the methane from the small grains, in particular less than 0.1 mm in size, prevails. The mass fraction of these grains in the total weight does not exceed 5%. For the typical parameters determining the mining, geological and technological conditions of methane emissions at different moments of time and position of the longwall were determined.