1.5% Methane or Above Normal Level at Grosvenor Mine Longwall Tailgate Roadway
Inspectors Marlborough and Gouldstone make the comment that the “normal methane level” in the Tailgate Rodway is 1.5% or above.
I assume this is when the face is not cutting.
If there is around 80 m3/s(cubic metres per second) of ventilation this equates to 1.2 m3/s of methane.
If 0.4 % is in the intake at the Maingate this is 0.32 m3/s of methane.
1.1% or 0.88 m3/s of methane is desorbing off the coal face and coming out of goaf.
To reach 2.5% methane from 1.5% in 80 m3/s of ventilation requires a further 0.8 m3/s (or 800 lites per second) of methane being released during the cutting process which includes the methane liberated when the coal is broken and crushed during the mining process.
The Inspectors note that the residual gas content at 2 m3/tonne 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%”.
This begs the question if Grosvenor mine has relatively low residual gas content compared to other underground mines who have very few or no methane HPI’s why does Grosvenor routinely have them?
What is so different at Grosvenor compared to other Underground Mines particularly thse operating in the Goonyella Seam?
While the comment about the residual gas content being low at 2m3/tonne may be true for the section of the coal seam being mined, but what about the floor coal?
In another part of the same Mine Record the Inspectors state the last 2 HPI’s appear to come from floor blowers
It was explained that the last two HPl’s appeared to be a result of floor blowers in the goaf These coincided with high loading on LW shields and it is believed that this loading may be as a result of the thickening of overlying sandstone in the roof strata. Analysis is being undertaken to verify this
The TG methane level sits at 1.5% or above as the normal methane level. We explained that this intake pollution is a significant cause of the high Methane level in the TG general body
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%
We made the following points in conclusion;-
- Intake pollution round the bleeder is a significant impact on the methane levels. This apparent with 04% showing on the MG methane monitor. The Mine should consider options for reducing this including reversing air around the bleeder or controlling the rib emissions by the application of Fibrecrete as has successfully been done at Moranbah North. This would benefit all subsequent blocks relying on the air from the bleeder.
