Goaf Differential Pressure Grosvenor Mine May 2018

By utilizing intake bleeder road ventilation around the perimeter of the sealed 101 Block there is a pressure drop from the both the active LW 102 Goaf and the Sealed 101 Goaf towards the Tailgate of LW102 Face effecting the whole of both the sealed and active goafs.

This ventilation design is maximising the amount of methane reporting to the Tailgate and exiting via the goafstream.

Also the intake air for longwall face (o.4% CH4) is being contributed to by intake air travelling by the bleeder road.

To try and offset the self-induced pressure drop and methane migration from 101 Sealed Goaf to 102 active goaf the mine is injecting Nitrogen into 101 Goaf as “Grasstree has successfully achieved”.

There is no mention about how long or what effect the Nitrogen Injection has had.

The principal of Nitrogen Injection into a sealed goaf requires that the is as minimal leakage and pressure difference is possible.

If the goaf is not sealed and if the goafs are interconnected through seal/strata failures then just the barometric effects completely overwhelm any effects of the relative miniscule quantity of Nitrogen injected versus the goaf void and gas quantities.

Out of the 22 Methane HPI’s for >2.5% in the Longwall Tailgate I am in possession of, none of the HPI’s ever mention either the Sensor on the Tailgate Drive, Shearer Sensor or #149 Sensor either approaching or exceeding 2%.

1. Grosvenor employs bleeder road ventilation. The ‘Bleeder Road” intakes air around the perimeter of LW 101 along the bleeder road, past active goaf seals and mixes with intake air from the travel road.
2. The TG methane level sits at 1.5% or above as the normal methane level. 04% methane intake pollution is a significant cause of the high Methane level in the TG general body.
3. The Mine is injecting Nitrogen into the 101 goaf in order to try to minimise methane migrating from the 101 goaf to 102 goaf as had been successfully achieved at Grasstree Mine
4. The goaf in the immediate tailgate area does not hang up and the goaf often rills in and impacts operation of/damages Chock #149
5. The residual gas content of the coal in 102 LW, where the face position is currently is approximately 2 m/t. This is not particularly high and mines with higher gas content are having very few or no methane issues in the TG resulting in HPl’s with methane greater than 2.5%
6. Grosvenor mine had reported 32 HPl’s since LW 102 had commenced production in January 2018. This represehted 60% of all HPl’s in Queensland associated with Methane greater than 2.5% in Longwall TG