Published in March 2008 Australian Longwall Magazine

Lying beneath the mountain range, the Pike River Coalfield is New Zealand’s largest known deposit of hard coking coal with an in-ground resource of 58.5 million tonnes.

ASX-listed Pike River’s mine plan targets production of about 17.6Mt over 19 years, with the potential to increase as further reserves are assessed in the deeper Paparoa coal seam.

The mine is on track to commence production late in July 2008 and reach full production during mid-2009.

Pike River Coal general manager Peter Whittall told that due to the nature of the physical environment at Pike River, conventional underground mining methods were uneconomical, and largely unable to be used.

“Longwall mining was not viable because of the slope of the seam and seam discontinuities,” he said.

“Continuous miners and a roadheader will be used to develop the roadways but the sloping seam does not allow for the large panel layouts of bord and pillar or longwall mines and the seam thickness would see too much coal wasted using only CMs for extraction.”

Instead, Pike River will employ a hydraulic mining method – which involves using high-pressure water from a hydraulic monitor (essentially water cannon) to cut and transport coal from either side of a pre-driven roadway.

The system requires a high-pressure pump to deliver water through the mine to the monitor nozzle. Discharge at the nozzle is approximately 2000psi (14,000kPa or 14MPa). The unit is designed to cut coal up to 40m away.

The main advantage of hydraulic mining is that it is a flexible system which can be applied to thick and moderately dipping seams.

There are no conveyors required in the mine and therefore roadways are driven to maintain a minimum grade rather than straight lines as in a longwall mine. This makes it more flexible in negotiating faulted ground. Plus, capital costs are minimal compared to a longwall, with the monitor unit itself only several hundred thousand dollars.

Pike River conditions suit the hydraulic method with its strong roof and floor to prevent collapse during extraction of the coal causing rock dilution in the coal; and strong but fractured coal to allow the coal to be easily cut but also to stand up during the cutting process and not collapse and inundate the roadway.

Pike River also has a good water supply as the monitor requires nine cubic metres per minute of clean water. Add this to the 4cu.m/min in each of the three development units and some other processing water and that means 23cu.m/minute (23,000 litres/min) of water is needed in the mine during peak production. Rainfall in the ranges of the Pike catchment is 6000mm per year.

New Zealand’s Solid Energy has used the hydraulic method at three of its west coast mines. The method was also used in Korea, Japan, Canada and Germany although none of these places are currently operating. A number of mines in China are still using hydraulic monitors although they are smaller capacity units.

As with any mining method, hydraulic mining is only effective with skilled operators. Maximising coal recovery without premature caving is a challenge for this method, especially if the operation wants to leave the top of the seam behind due to higher ash or sulfur.

Pike intends to house the monitor unit within a breaker line support which will provide ease of mobility and also greater operator safety at the goaf edge. Coal from the face area will be directed into steel flumes (as will coal at the back of the continuous miner units), which are approximately 500m wide by 500mm high. The open steel troughs will flow the coal downhill to the pit bottom where it will be further crushed to less than 35mm and then pumped in an 11-inch steel pipeline about 10km down the access tunnel and along the mine access road to the coal preparation plant.

Pike River Coal has unique properties, such as low ash levels and high fluidity – highly valued by international coke and steel companies.

The company has already secured conditional contracts for significant supply to international coke and steel companies, including supply to its Indian shareholders, Saurashtra Fuels Private Limited and Gujarat NRE Coke Limited.

Pike River is currently developing a specialised training system for the hydraulic monitor and standard training will be used for the more common equipment. The company said the recruitment campaign to attract skilled workers had so far been successful.

“The fact that Pike River Coal is a greenfield coal mine with 100 percent new equipment is a real attraction. Being located in a magnificent tourist destination is also a plus,” Whittall said.

For Whittall this project has been a great opportunity to build on and utilise many engineering and project experiences.

“Having the opportunity to help build a new mine with Pike River Coal is allowing me to use many of the lessons from the Dendrobium start-up and from Illawarra Coal, and also much of the knowledge I gained from working with some excellent project managers and engineers,” he said.

Pike River Equipment

• Waratah Engineering: 1 roadheader, 2 continuous miners
• Specialised Mining Vehicles: 4 man transporters, 3 Brumbys
• Juganaut Industries: 2 LHDs
• Ampcontrol International: 4 flameproof substations, 4 flameproof DCBs, 3 flameproof section isolators
• Flakt Woods: Mine ventilation fans
• Weir Minerals Australia: 5 slurry pumps, 4 make up water pumps, 5 fluming pumps
• WCCC: Transport services agreement
• Evan Jones Construction: Surface buildings
• Brightwater-PEAT: Coal preparation plant
• McConnell Dowell: Tunnel
• White Night Joint Venture: Roads