The Impact of Air Velocity on the Formation of Methane Concentration Fields in Excavated Workings

The article addresses a significant aspect of ventilation in excavated workings with the influx of hazardous gases. The selection of appropriate ventilation affects worker safety and helps avoid localized accumulation of gases at dangerous concentrations. Polish mining regulations allow methane accumulation in roadways of up to 3%, which provides a safety margin relative to the methane explosibility limits of 5–15% CH4. The methane concentrations obtained in the study ranged from 0.3% to 1.39%. The presented studies focused on the impact of air velocity on the formation of methane concentration fields. For this purpose, a numerical model was created based on an underground measurement results obtained in the active roadway with confirmed methane influx. The analysis of methane concentration distribution in the excavation was conducted using Ansys Fluent 2024 R1 for three different air velocities in the whirl flow airduct. It was shown that within 30 m from the face, the methane–air mixture is heterogeneous. Beyond this distance, it becomes a homogeneous mixture, regardless of the air velocity supplied by the auxiliary ventilation. Additionally, the occurrence of air recirculation was observed, resulting from the typical arrangement of equipment in the excavation space. The presence of elevated methane concentrations in the zone between the whirl flow airduct and the adjacent excavation floor is a notable phenomenon.