Optimising adjacent goaf drainage operations by utilising automated control logic at Kestrel South Mine

Seal leakage contributes significantly to methane emissions during longwall mining, occurring when a sealed goaf pressurises with coal seam gas from overlying seams within the sealed goaf subsidence zone, which then leaks into the tailgate roadway. This paper aimed to minimise methane seal leakage in an active tailgate by optimising sealed goaf drainage and its influence on nitrogen inertisation. Optimisation occurred through developing an automated control system that varied sealed goaf drainage quantity in response to variable barometric pressures. The methodology analysed the adjacent goaf drainage operations at Kestrel South Mine, utilising goaf wells on the tailgate side of the adjacent goaf and applying suction to the sealed area alongside nitrogen inertisation through a tailgate seal. The control system utilised a Proportional - Integral - Derivative (PID) control-loop utilising a real-time differential pressure sensor on a tailgate seal as a feedback loop. The project found that adjacent goaf drainage operations could not effectively manage seal leakage during longwall startup. However, when ~900l/s of sealed goaf drainage and ~600l/s of nitrogen inertisation was achieved, seal leakage rates stabilised below 0.2% CH4 concentration in the tailgate roadway. The control system reduced sealed goaf drainage quantity when tailgate seal pressure was <200Pa, reducing the risk of spontaneous combustion and maximising the current goaf drainage network capacity.