Underground » Ventilation, Gas Drainage and Monitoring
In gassy underground coal mines prone to spontaneous combustion, goaf management is a challenging task to reduce the risks of gas explosion and spontaneous combustion to acceptable levels. Goaf gas drainage via vertical surface goafholes is a primary control method to manage gas emissions in Australian coal mines. However, the performance of vertical surface boreholes may be significantly limited by an insufficient understanding of goaf gas flow and coal self-heating behaviour, especially under intensive goaf gas drainage. As mining operations reach greater depths and produce more gas emissions, the spacing between vertical goaf gas drainage boreholes has been narrowed, and suction pressure has increased. Goaf drainage capacity in some Australian mines has reached 20,000 l/s, which concurrently alters goaf pressure distribution and gas flow patterns. This alteration leads to the potential for increased air leakage into the goaf and the associated increase in the risks of spontaneous combustion and gas explosions.
As an extension project to project C29017, this research further analysed field goaf gas drainage data from various coal mines across Australia to establish the typical gas composition trend of goaf atmosphere and proposed the goaf gas conceptual model under the impact of goaf gas drainage.
Additionally, this project focuses on developing Computational Fluid Dynamics (CFD) models to understand goaf gas flow patterns with operating vertical boreholes, calibrated using back analysis results. The simulation results from the calibrated CFD model align well with the goaf conceptual model based on field gas drainage data. The ventilation air leakage originating from the longwall face flows along the maingate side goaf for a certain distance, travels through high-permeability channels to the tailgate side and is finally extracted by goaf gas drainage boreholes.
These findings provide engineers a visual understanding of the ventilation airflow pathways within the inaccessible longwall goaf under the impact of intensive goaf gas drainage in gassy mines. Moreover, this study conducts a comparative analysis of goaf atmospheres, gas explosion risks, and sponcom risks across various scenarios through CFD simulations. It also facilitates an understanding of the varying sensitivities among different goaf characteristics, including goaf permeability distribution, gas emission rate, and goaf gas drainage parameters.
These findings offer mine operators valuable insights to enhance goaf gas drainage performance by integrating field monitoring data analysis and CFD simulations. Prioritising safety in mining operations and minimising environmental impact through effective management of gas emissions, this study lays the groundwork for advancements in sustainable mining practices.