Analysis of The Effects of the Position of the Air Duct Supplying Fresh Air to the Working Face of the Mined Dog Heading on Methane Concentration Levels

Abstract

Each year, more than one hundred kilometres of new dog headings are mined in underground hard coal mines. Such headings are ventilated by means of an air duct system. A stream of fresh air is supplied to the working face of the mined heading through an air duct with a view to ensuring proper chemical composition and temperature of the mining atmosphere. This is because this heading is being exploited and the ventilation must provide adequate working conditions for the crew. While dog headings are being mined in the body of coal, they are additionally filled with methane, which is released in this process. Due to the risk of its combustion and explosion, methane is a highly dangerous gas. It represents one of the greatest hazards in underground mining. Therefore, a particularly essential issue during the mining of dog headings is to reduce the potential for dangerous methane concentrations to occur. To prevent this from happening, it is necessary to select adequate parameters for the fresh air supplied through the air duct and the position of this air duct. It is the position of the air duct that appears to be a very significant element in the ventilation process of dog headings. Model-based tests were conducted to determine how the position of the air duct affects methane concentration levels. Their results have been presented in the paper. The tests were conducted using Computational Fluid Dynamics (CFD). The related calculations were performed in ANSYS Fluent, based on the finite volume method (FVM). The analyses performed made it possible to identify the concentrations levels of methane and the physical parameters of the flowing gas mixture at each spatial point of the area under examination, for the boundary conditions adopted. The purpose of the tests was to determine whether and to what extent the position of the air duct, which is used to supply fresh air to the mined dog heading, influences methane concentration in this heading. The tests were conducted for an actual mining region in which a dog heading was mined. The input parameters for the model (boundary conditions) were therefore adopted from the actual system. The model-based tests helped to determine the distributions for methane concentration depending on the position of the air duct. The analysis mainly encompassed the distance between the outlet of the air duct and the surface of the mined body of coal. The use of model-based tests which employed numerical methods made it possible to determine a series of significant physical and chemical parameters of the resulting mixture of gases. Their distributions and values in selected points for the variants under analysis have been presented in the paper. The results obtained unambiguously demonstrate that the position of the air duct has a significant impact on the distributions of methane concentration levels in the mined dog heading. In the Authors’ opinion, these results may constitute an essential source of information for service teams responsible for ensuring ventilation-related safety in mines. This is because they allow for predicting the distribution of methane concentration and other parameters of the gas mixture that occurs in dog headings during the mining process.