Features of the calculation of air leaks through the mined-out space of coal mines

Abstract

The movement of air leaks through the goaf of coal mines can lead to gas contamination of workings with the formation of local and layer accumulations of methane. This increases the likelihood of explosive situations. Therefore, an important factor is the ventilation scheme used in the excavation area. The process of gas flow through a goaf is an understudied issue. This is due to the difficulty of conducting direct measurements inside the object under study. In many works, when studying the movement of air leaks through the mined-out space, the linear Darcy filtration law is used. However, the influence of inertia forces can lead to additional gas pressure losses and, accordingly, to deviations from the classical law. Therefore, it is advisable to use the law of two-term filtration. The purpose of the work is to study the patterns of movement of air leaks through the mined-out space, taking into account its filtration parameters and the current ventilation scheme. The article presents the results of calculating the speeds of air leaks and the trajectories of streamlines in the mined-out space with direct-flow and return ventilation schemes. The Darcy formula and the Forchheimer formula were used in the calculations. It has been established that with a two-term filtration law, the values of the result-ing air leakage rates are less than with a linear law. This is due to pressure losses as a result of inertial forces. It has been established that with a direct-flow ventilation scheme, the rates of air leakage in the longwall increase exponentially along the goaf boundary in the direction of the ventilation flow and quadratic ally increase deep into the goaf to a certain maximum located at a distance of about half the length of the longwall. At the same time, in the case of the return-flow ventilation scheme, the rates of air leaks in the longwall have maxima at the boundary of the goaf and decrease linearly towards the center of the longwall, and in the goaf at a distance of up to three meters from the longwall, their quadratic decrease occurs. The results obtained make it possible to reduce the gas contamination of workings by choosing rational schemes and ventilation modes.