STUDY OF METHANE FLOW IN CAVED GOAFS AJACENT TO LONGWALL FACES IN VALEA JIULUI COAL BASIN

Methane emission in the working face area within a colliery is a complex phenomenon, depending on a large number of geological, technical and mining factors. The ever increasing mining depths in the collieries from Valea Jiului hard coal basin is rendering more and more difficult the challenge of properly insulating active mine workings from the caved goaf. Air leakages through the goaf are directly contributing to migration of methane stored from undermined surrounding rock bed. This process also hinders the face line advancement speed to increase, potentially generating explosive hazard related to flammable gas mixtures. The adequate use of a methane gas emission regime forecast method and a proper knowledge of the complex methane emission mechanism should allow the development of improved technical means aimed at safe and sound underground ventilation management. Unfortunately, the most severe accidents occurred during the last two decades in this Romanian coal basin were triggered by methane accumulated in the caved goaf. Having as goal the safety level increase in underground mine operations, the paper highlights the results of an analysis on the gas dynamics behavior in caved goafs nearby operating longwall faces. Based on methane flow balance, a graphical dependence is obtained to express the allowable methane concentration within the goaf for the specific conditions met in longwall coal faces from Valea Jiului. The findings are a scientific ground for further improve the technical solutions of health and safety provision for all personnel and staff members working in the face, in the main return or in adjacent areas.