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Ventilation System Design Longwall Operations At Grosvenor Mine 9th May 2018

Ventilation System Design Longwall Operations at Grosvenor Mine 9th May 2018

The basic design philosophy and practice of the ventilating of the Longwall face is mentioned in the Inspectorates Mine Record Entry.

I do not have a Mine Plan so am unsure of the exact location of the intake shaft in relation to the bleeder road and longwall face.

I assume the following is the case.

The ‘Bleeder Road” shaft intakes air along the bleeder road, past active goaf seals and mixes with intake air from the travel road. (I have been informed approximately 25 to 30 m3/second)

The mixed “intake” air then splits at the belt road with the majority reporting to the Maingate of the Longwall (approx 80 m3/s) and sufficient returning along the belt road keep the belt road below 1.25%.

The reason Inspector Marlborough is asking about whether the bleeder road can be turned into a return is to change the differential pressure differences in the active goaf.

Changing the bleeder shaft to a return shaft will dramatically change the pressure balance of the goaf.

Gas migrates from higher pressure to lower pressure.

The current design of the mine maximises the pressure differential at the Tailgate of the Longwall.

Intaking around the perimeter of the goaf in itself automatically pulls methane from the back of the goaf towards the Tailgate

Turning the “Bleeder Road” shaft into a return would have the effect of lowering the quantity of methane reporting to the tailgate and lower methane concentrations.

In reality pulling the explosive fringe further away from the tailgate drive and shearer.

Inspector Marlborough makes the following comment

The Mine must consider the level of risk in determining whether or not reversing the bleeder road ventilation presents an acceptable level of risk.

My only comment in this post is

There cannot be a methane explosion without an explosive mixture of methane being present and then introducing an ignition source.

Obviously designing and operating the ventilation system to deliberately lower the existing goaf pressure differentials and lowering intake methane contamination as well as face emissions is beyond them.

There are several more points in this MRE that need to be dealt with in seperate posts

 

Mr Webber stated that they had completed a risk assessment on putting the bleeder road onto return but that to do so the conveyor would have to be put on intake, which could cause other issues such as heat and dust on the LW face.

The MG AFC methane monitor shows approximately 0.4% Methane. 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 Mine must consider the level of risk in determining whether or not reversing the bleeder road ventilation presents an acceptable level of risk.

  • 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.
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