Proactive goaf inertisation for controlling longwall goaf heatings
Deep oxygen ingress into the goaf can lead to spontaneous heatings particularly during face stoppage or slow face retreat in the panel. This requires the deployment of proactive goaf inertisation strategies based upon detailed understanding of goaf gas flow patterns and distribution characteristics. An integrated approach combining goaf gas monitoring, Computational Fluid Dynamics (CFD) and field trials has been used for the development of effective goaf inertisation strategies in underground coal mines. CFD simulations indicate that inert gas injection close to the face is ineffective even at higher flow rates in the order of 1.0 to 2.0m3/s. Inert gas needs to be injected at 200m to 400m behind the face at the rate of about 0.5m3/s to achieve effective goaf inertisation in most cases. Proactive inertisation strategies developed during the course of the study were highly successful in reducing oxygen ingress into the goaf and in achieving effective goaf inertisation by reducing oxygen levels below 5% at 200m behind the face. The study also indicates that just injecting inert gas into the goaf does not ensure prevention of heating incidents in the entire length of panels or all longwall panels. A number of parameters such as panel ventilation system, goaf caving conditions, and longwall retreat rate and goaf gas drainage can make a specific inertisation strategy ineffective and the inertisation strategies need to be modified based on the specific conditions at the mine sites.