Mine Record Entry March 16th 2018
MRE – Grosvenor Coal Mine – 16.03.2018
Between the 4th of March and 6 am on the 14th of March, there are Eight (8) Methane HPI’s.
There are another 4 before this Mine Record Entry is sent.
In the Inspectors own words
LW102 has experienced numerous HPI events since it commenced production associated with Methane in the TG exceeding 2.5%.
Many of these seem to be associated with advancing the TG shields but others do not appear to be related to this.
Roof conditions in the LW TG immediately outbye of the TG shields are causing excessive flushing around the TG shield and the goaf is typically caving hard up behind the TG shields.
The mine has formed an incident Management Team to address the problem, but repeated events of Methane in excess of 2.5% in the LW TG have been occurring.
The Inspectors are not goimg to the Mine till the 19th of March when they were due to conduct the Safeguard Audit of PHMP for Gas Management.
The Inspectors note the last five goaf drainage holes (50m spacing) have not come on line and are not draining methane from the goaf
They pose a number of queries about the principles of direction and speed of longwall mining operations and the design of the ventilation system..
These include
- turning the “bleeder road” into a return so as to try and pull the goaf gas fringe back from the Tailgate end of the Longwall.
- Lowering the Quantity of ventilation across the face to lower the pressure differential from Maingate and tailgate. Again with intention of having the goaf gas fringe pull back from the Tailgate end.
Grosvenor seems to run around 80 m3/s (cubic metres per second) across the Longwall Face.
If the quantuty was reduced to around 56 m3/s the pressure differential between the Maingate and Tailgate would be halved. (P=RQ2) Pressure equals Resistance multplied by the Quantity Squared)
Inspector of Mines Les Marlborough, Richard Gouldstone and Paul Brown have been involved in several discussions with Grosvenor Mine management during the period from 14 March 2018 to 16 March 2018. These discussions have been in relation to the issues that the Mine has been having with Methane management in the LW102 TG. LW102 has experienced numerous HPI events since it commenced production associated with Methane in the TG exceeding 2.5%.
Most of these are as a result of the failure of the goaf drainage system to effectively remove methane from the LW102 goat. The mine now has 5 goaf drainage holes immediately behind the Longwail that have failed to come on line and to draw gas from the goaf. These holes were drilled at a 50 m spacing. The mine has formed an incident Management Team to address the problem, but repeated events of Methane in excess of 2.5% in the LW TG have been occurring.
Many of these seem to be associated with advancing the TG shields but others do not appear to be related to this.
Roof conditions in the LW TG immediately outbye of the TG shields are causing excessive flushing around the TG shield and the goaf is typically caving hard up behind the TG shields.
During the discussions the Inspectors have raised several items for consideration;
Putting “bleeder road” onto return to create a negative pressure across the goaf to draw the gas fringe away from the TG end;
Applying suction to inertisation lines in goaf seals behind the LW after bleeder is put on return;
Reducing cut rates;
Uni Di vs Bi Di
Cutting TG at half web to minimise flushing;
Bailing of existing goaf holes as they pass over the TG end until they come on line;
Are the methane trip levels in the TG appropriate?;
Altering ventilation quantity across face;
Is inertisation being applied to LW102 Goaf? If so, is this pushing gas to TG end?;
The mud that is being found in the failed goaf holes, has this been analysed to determine source?
Drilling holes closer to top of coal seam;
Lined vs unlined holes;
Positioning of goaf holes in relation to TG.
A meeting has been arranged at the Mine on Monday 19 Mar 2018 at 13:00 to discuss the status of the mine and the actions being taken to address the issues. Inspectors Marlborough, Gouldstone and Brown will attend along with Grosvenor Management representatives.
