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IMPACT OF THE PERMEABILITY OF GOAVES WITH CAVING ON THE METHANE CONCENTRATION LEVELS IN THE UPPER CORNER OF A LONGWALL

Magdalena Tutak

Abstract

The methane hazard is one of the main natural hazards occurring in underground hard coal mining. This hazard is related to the potential ignition and/or explosion of methane when mixed with air. The underlying cause of this problem is methane release from the body of coal, the goaves with caving and the excavated coal area. The region most vulnerable to this hazard in coal exploitation during longwall ventilation using the U-type system from the exploitation field borders is the intersection of the longwall and the airway (the so-called upper corner of the longwall). The accumulation of methane in this area results from its outflow from the goaves with caving. The amount and dynamics of methane release from the caving zone depends not only on the methane content of the seams lying over and under the caving goaves of the exploited longwall, but also on the permeability of these goaves and the type of roof rocks forming the caving. The release of methane from the goaves with caving is boosted by the partially degassed subeconomic seams found in such goaves as well as by the fractured and permeable rock mass around them. The permeability of the goaves causes gases to flow through the caving zone, thus leading to an outflow of methane into the working area of the longwall. The article demonstrates the results of model-based tests aimed at determining the influence of the permeability of goaves with caving on the methane concentration levels in the upper corner of the longwall ventilated by means of the U-type system from the exploitation field borders. It should also be emphasised that the permeability of goaves depends on the stratification resistance of the caving rocks. The analyses carried out made it possible to determine the distributions of methane concentrations at the outlet from the longwall for specific mining and geological conditions as well as for various roof rocks forming the goaves. The results obtained should have a wide range of practical applications.

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DOI resolver: doi.org/10.5593/sgem2018/1.3/s03.062

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