Methane level in the Tailgate Roadway General Body is greater than 2.5%, yet at the tailgate drive methane is typically 0.5% or less. What affect do Three venturis and two ventilation curtains face side have?
One matter that deserves discussion is Inspector Marlborough about how the methane level in the Tailgate Roadway General Body is greater than 2.5%, yet at the tailgate drive methane is typically 0.5% or less.
Inspector Marlborough does not take into account is the outcomes of what appears to be the Grosvenor Standards as documented in previous Mines Inspectors MRE for the use of
Brattice wings to control the methane in the Tailgate drive, and
Three venturis and two ventilation curtains face side were set up to assist in dispersing methane flushing from the goaf on the last 60m of faceline“.
For those unfamiliar with venturi’s.
Pneumatic venturi air movers have no moving parts and simply require a supply of clean dry compressed air. Primary air enters the rear manifold and is released through the centre.
Secondary air is drawn into the centre and mixes with the primary air stream and exits through the front at a higher velocity.
Therefore any methane sensor placed directly outbye the direction the venturi is pointed and directed will will also have a diluted methane concentration.
All the methane detector measures is the methane concentration where the sensor head is located
This can/does create a situation that the methane sensor readings at the Tailgate Drive are not a true indication of the methane General Body readings at the Longwall tailgate drive and can be/are in fact much below what the Tailgate Drive is truly exposed to.
Inspector Marlborough stated this in his MRE from the 13th September 2017.
MRE – Grosvenor Coal Mine + comments shearer sensors – 13.10.2017.pdf
As can be seen from the sketch, when there is a situation with greater than 2.5% Methane in the TG general body, the Methane reading on the TG AFC and Shearer monitors are typically 0.5% or less.
This means that the bulk of the Methane reporting to the Tailgate Roadway is being swept out from the goaf fringe by the air stream that is deflected round the shearer as it travels into the TG end.
It will be highly likely that this Methane rich air stream will be in excess of 5% Methane and will flow over the TG shearer drum, which normally has to cut approximately 1.5 m beyond the end of the TG AFC Drive to trim the floor to allow the drive to be advanced.
The use of venturi’s and ventilation curtains is contained in the MRE of Inspectors Richard Gouldstone and Paul Brown in August 2016.
MRE – Grosvenor Coal Mine Methane LW face – 05.07.2016.pdf
The MRE also notes that “there was a pick-up of methane from 0.2 to 0.5% along from MG to TG on the face”
This MRE details that LW 101 has retreated approximately 240m about 60m short of ‘square’.
Just to show that nothing much changed from 2016 till 2020
- Roof control problems have been encountered particularly at the tail gate end of the face.
- Methane goaf well holes being slow to “become productive”
The fall was not presenting any significant obstruction to ventilation and questioning of the official revealed that there was a pick-up of methane from 0.2 to 0.5% along from MG to TG on the face.
Three venturis were set up and two ventilation curtains face side to assist in dispersing methane flushing from the goaf on the last 60m of faceline.
Goaf holes have been spaced at 50m and some difficulty has been experienced with n07 hole being slow to become productive.
Brattice wings to control the methane in the Tailgate drive were contained in now Deputy Chief Inspector Dobson’s MRE for the 21st of September 2016
21.09.2016 Dobson MRE – Grosvenor Coal Mine –
The effect of the compressed air venturi’s and ventilation curtains is readily apparent from the Gas Readings recorded by Inspector Dobson.
The methane level is 0.2% at the tailgate drive while the general body in the TG return is 1.75%.
The Oxygen level remains constant.
As Inspector Gouldstone notes in his MRE in August there was a pick-up of methane from 0.2 to 0.5% along from MG to TG on the face.
Assuming the same condition of methane being 0.5% at the Tailgate of the Longwall a month later, how is it possible for there to only be 0.2% at the Tailgate Drive?
Tailgate General body from his earlier inspection which was as follows:
- Methane – 1.75%
- Oxygen — 20.1%
- Carbon Monoxide — Ippm Hydrogen Sulphide — Ippm Nitrogen Dioxide — 0.1 ppm
He then took a reading at the rear of Tailgate drive
- Methane — 0.2%
- Oxygen — 20.1%
- Nil other gases detected
I then discussed with the ERZ Controller the environmental conditions on the Longwall with regards to recent Methane issues on the Longwall.
He explained about the use of brattice wings to control the methane in the Tailgate drive area and the use of goaf wells at 50 metre spacings in the Tailgate to assist in reducing the general body methane make.
I asked if he had inspected the Tailgate which he confirmed and provided his personal gas monitor readings for the Tailgate General body from his earlier inspection which was as follows:
- Methane – 1.75%
- Oxygen — 20.1%
- Carbon Monoxide — Ippm Hydrogen Sulphide — Ippm Nitrogen Dioxide — 0.1 ppm
- Ventilation quantity — 82 m3/s
- Ventilation velocity — 5.5 m/s
He then took a reading at the rear of Tailgate drive
- Methane — 0.2%
- Oxygen — 20.1%
- Nil other gases detected
Outbye of the Tailgate drive I asked him to measure the ventilation velocity which was 6.1 m/s.
Visible dust that was apparent in the general ventilation stream whilst coal cutting activities were being undertaken appeared visibly excessive and this was still the case when operations stopped due to an outbye conveyor issue.
