Published in March 2006 Australian Longwall Magazine

The operation worked together with the QMRS, inertising a section of the mine in 24 hours. The trial was also used to validate ventgraph models and assist with the application of the GAG at the Northern Underground.

The main mine fans were turned off around 8:30am on December 15 and ventilation was basically suspended in the mine workings whilst the shaft cap was fitted. The GAG port was fitted to the top of the shaft to allow the GAG hook-up to take place later in the day.

Seal site ventilation was established using an 80m3/sec fan located at the top of the old belt drift and the outbye part of the mine was effectively ventilated at the same time.

The GAG injection process commenced at 4:30pm the same day and products of GAG combustion were noted on the mine monitoring system at the bottom of the shaft around 45 minutes later.

Injection continued until around 2:40am on December 16 when the GAG was stopped due to a minor mechanical failure.

During the GAG injection process, the quantity of material exiting the workings at the D heading seal site was measured at around 6.5m3/sec. This low flow was due to a combination of contraction of the exhaust gas due to cooling, the loss of water vapour out of the mixture, the flow of air into the sealed areas due to a barometric high and the effect of turning off the main mine fans.

The door in the temporary seal was closed at 4:30am on December 16 and final sealing continued at that site until the D heading seal was completed at around midday on December 17.

At 6:30pm on December 18, the underground atmosphere was showing a gradual increase in methane across the board. At no point had the atmosphere gone explosive. Newlands management said the methane concentration had been steadily rising and it appeared if it did go explosive, it might just pass through the bottom corner of the Cowards triangle.

During the operation, underground gas readings were taken with a tube bundle. They showed that the shaft bottom area inertised within a suitable time frame, but the gas did not migrate throughout the remainder of the mine as predicted.

Newlands Underground operations manager Dave Stone said the main issues during the operation were cooling of the gas which reduced the quantity (80C to 35C), leakage into the goaf and back pressure from the buoyancy of the gas in the shaft.

He also said they were still undecided whether they would use the GAG method of mine sealing in future.

“The use of the GAG appears to be very situational-specific. All factors are required to be analysed prior to the use of the GAG, and the Northern Underground operation is currently assessing various scenarios for which the GAG would be applicable,” they said.

Newlands mine management is currently preparing a position paper that discusses the use of the GAG at the Northern underground, taking into account the results from the Southern Underground.