Underground » Detection and Prevention of Fires and Explosions
The main objective of the project was to develop optimum and effective strategies for inertisation during longwall sealing operations to achieve goaf inertisation within a few hours of sealing the panel. The project has combined the detailed analysis of the performance of various inertisation field trials together with computational fluid dynamics (CFD) modelling of different inertisation operations in order to develop the optimum inertisation strategies. The project work specifically involved review of the current inertisation practices, laboratory studies, CFD simulations, tracer gas tests and field demonstration studies.
Analysis of the data from six review case studies showed that the traditional inertisation schemes were not effective in preventing the formation of explosive gas mixtures in three cases, and in the other three cases oxygen concentration levels were above 12% for up to two days after panel sealing. CFD modelling simulations and review studies indicated that just injecting inert gas through the MG or TG seals does not achieve quick inertisation of longwall goafs. Based on the results of various simulations, an optimum inertisation strategy was developed taking into consideration the positive effects of various options and the field site conditions. Field demonstration studies of the optimum strategy were conducted at Newlands Colliery in Queensland.
The recommended guidelines for optimum inertisation strategy are:
- inert gas should be injected into the goaf at 200 m behind the face finish line, i.e. at an inbye location with respect to explosive fringe in the goaf.
- inert gas should be injected on the intake side of the goaf OR on both sides of the goaf, if possible.
- inert gas injection should start at least 1 or 2 days before panel sealing, with minimum ventilation flow and doors on the return seal still open.
- inert gas flow rate of 0.5 to 1.0 m3/s is recommended, subject to implementation of all these optimum strategies.
- inert gas injection to be continued after sealing until O2 levels are below 8%.
During the field demonstration studies, the goaf atmosphere was inert by the time of closing the doors on the final seals, with oxygen concentration below 5% at all locations in the goaf. The project demonstrated that the new optimum inertisation strategies developed were highly successful in converting the goaf environment into an inert atmosphere within a few hours of panel sealing.