Throughout the history of mining, methane, which is a highly explosive gas with an explosive range of 5% to 15% in air has always been a major problem to the people working underground. Ventilation is the primary requirement for keeping the methane levels below the safe level of 1.25%. Thousands of explosions have occurred due to badly planned or insufficient ventilation in coal mines. When planning a mine, the fresh air drawn through the pit has to be of sufficient pressure and flow to remove the gases produced underground and keep them within set safe limits. There are many parts of a mine ventilation system used to achieve this including, the main fan, auxiliary fans, booster fans, air doors, regulators and air crossings to name a few.
When a coal face is mining, billions of cubic litres of methane are produced which has to be safely managed. The main way of achieving this is to supply vast quantities of fresh air at sufficient pressure and flow to deliver the quantity to dilute the methane passing through the face. The Selby Coalfield main fans were very powerful at 2,100kw and could draw upto 360 cubic metres of air per second around the mine to achieve the quantities needed.
A further control measure is to stop the methane getting into the air flow in the first place by drawing the gas from the strata above and below the working coal faces and sending it to the surface in pipes. This process is called Methane Drainage. The Barnsley seam worked in the Selby Coalfield is famously very gassy so Methane Drainage was planned during the design of the complex.
Riccall Mine used the same system of Methane Drainage during the life of the pit. The tailgate of every face had a system of boreholes drilled into the gob at a minimum distance of 10m at the back of the face line. This distance allowed for the strata in the gob to fracture and settle. If the holes were drilled too close to the faceline the standpipes were prone to being sheared when the gob settled. The system described below was used on all faces at Riccall Mine with the exception of East side of the pit.
Methane borers drilling top holes with mini Hydrac Drill Rig.
The top drainage holes were drilled at 60 degrees towards the gob every 15m in the tailgate roadway. The holes were bored using 18 x 2 feet 6 inch drill rods. The 18 x 2 feet 6 inch drainage standpipes were then installed into the hole with denso tape on each joint to seal the pipe into the hole. A stuffing box was then installed on the last pipe. The next stage was to drill a 50mm hole up through the standpipe with a further 42 x 2 feet 6 inch drill rods added onto the length of the hole giving an overall drilled length of 150 feet. This was called the production length and passed through the next 2 seams above the Barnsley seam called the Dull and Kents seams. The standpipe end was then connected to the methane drainage pipe range using a flexible 2 inch rubber hose. A hole was manually drilled into the methane range for a threaded connector piece for the pipe connection.
The methane borers had to work at the back of the faceline so ventilation was very important. The tail gate end of the face had steel reinforce supports called Fibcrete chocks installed as the face retreated. An anti static sheet, was fixed to the Fibcrete chocks, which regulated and directed the ventilation into the area at the back of the faceline where the borers were working.
The bottom holes were drilled at 60 degrees downwards towards the face every 40m in the tailgate roadway. The hole was drilled as above but only 8 x 2 feet 6 inch standpipes were installed with a stuffing box on the last pipe. The pipes on the down holes were sealed with oil well cement to ensure there was no water ingress from the lower strata. The 50mm diameter, production length was then drilled to an overall length of 150 feet passing through the Dunsil and Swallow Wood seams. The same process as above was used to connect to the pipe range. The methane drainage pipes were called pipe “A” and “B” and were 8 inch in diameter. Pipe range “A” was the ex compressed air range used for the heading development. Pipe “B” installed by the methane borers just before the face started production. Both pipes were laid in the rib side as the face retreated.
Hydrac Drill Rig and Power Pack.
The machine used to drill the drainage holes was called an E.D.E.C.O. Hydrac Drill Rig. Hydrac rigs were designed to have a drill stroke of 2 feet 6 inch to accept the drill rods of that size. A mini Hydrac rig was designed to have a drill stroke of 1 foot 3 inch for very confined spaces and heavily weighted roadways. The rig was supplied by hydraulic hoses from a pump which was situated slightly outbye of the faceline.
The transition from arch girders as primary supports to full roof bolting made a huge difference to working conditions for borers. The tail gate area became very confined and difficult for the lads doing the boring especially when working in the east of the pit due to the depth of the seam.
H472s tailgate using arch supports.
H475s tailgate with roofbolt supports.
Due to the difficulty and confined work and having to man handle the hydraulic rig, a specially designed hydraulic portable rig was designed for use in the Stanley Main seam in 2002. It was obviously called “The Moon Buggy”.
E.D.E.C.O. portable Hydrac rig (Bigbird’s Moonbuggy) used on SM 501s.
The 2×10 inch pipes with the trouser leg adaptor pipe at H504s Tail Gate end.
Due to the huge amount of methane produced at the east side of Riccall Mine the system was upgraded by using larger, 3 inch diameter standpipes, 65mm diameter borehole production length and 2 x 10 inch diameter methane ranges. The 14 inch pipe used in the return roadway was also upgraded to a GRP pipe.
At the outbye end of the tailgate, the two methane pipes were connected to the main methane range via a connector called a trouser leg. This pipe was 14 inch in diameter with methane monitoring sample tubes, pressure gauge, and manometer for testing purposes. The 14 inch methane range was installed in the return roadway and delivered the gas to the surface methane plant via No2 upcast shaft.
The surface methane plant contained four, Nash Vacuum pumps. The pumps operated automatically due to demand and were initially designed to vent the methane gas into the atmosphere.
In the early 1990s, the methane was used to generate electricity. The gas was sent to a separate filtration unit and gas turbine generator, manufactured by Dale Engineering.
Information kindly provided by my mate, Glenn Bryan ( Big Bird ) who worked as a Methane Borer on every face at Riccall Mine.
Selby Superpit 