Gas Management and Risk Mitigation Strategies for Longwalls

The main objective of this project was to develop optimum goaf gas management and risk mitigation strategies for highly gassy longwall mines. The project aimed to obtain a fundamental understanding of the effect of various parameters on goaf gas distribution patterns and investigate the performance of novel goaf gas drainage concepts, designs and strategies in order to develop effective goaf gas management strategies for highly gassy mines. Work involved modelling investigations, field studies, data analyses and demonstration of optimum gas management technologies and strategies at highly gassy mines. The project also aimed to provide greater insights into goaf gas migration patterns under different scenarios of main fans failure, large barometric pressure variations and major goaf falls, and an assessment of the risk of irrespirable atmosphere prevailing on the longwall face through transient modelling analyses.

A number of modelling studies were carried out to obtain a fundamental understanding of the goaf gas flow distribution patterns under different mining and operational conditions. Analyses of the results indicated that the oxygen distribution pattern in the longwall panels with steep gradients would be entirely different from the oxygen distribution pattern in the longwall panels with flat seam gradients. Results indicated that oxygen ingress would be high on both sides of the panel under flat seam gradients when compared with high oxygen ingress only on the maingate (MG) side of the panel under steep seam conditions. These goaf gas distribution patterns would have significant effect on goaf gas drainage efficiency and strategies.

Based on the analyses of the results of simulations, risk mitigation strategies have been developed to minimise the risks associated with fans and goaf plants failure, barometric pressure changes, and goaf falls. High goaf gas drainage rates and deep goaf gas drainage strategies would assist in minimising the impact of barometric pressure changes, fans and goaf plants failure, and goaf falls in highly gassy mines. Goaf gas drainage rates should be maintained at highest level possible through implementation of the recommended goaf gas drainage strategies to achieve total goaf gas drainage/ capture efficiencies of more than 80%. Longwall face ventilation/airflow should be maintained at higher flow rates to minimise the risks associated with fans and goaf plants failure, goaf falls, and barometric pressure changes.