Pillar extraction is back on the agenda again and NEPEAN Longwall is proving the coal mining doubters wrong with an ambitious and innovative project that, it says, may lead to an industry step-change, prolonging the life of underground operations by supplying a system that combines elements of both longwall and room & pillar mining methods.

Australia-based NEPEAN Longwall has a value proposition that spans all aspects of longwall mining equipment, including armoured face conveyors, beam stage loaders, shearers, drive units, electro-hydraulics, chain and flights, hoses, cables and other specific componentry.

It is known the world over for its tailored engineering capability, and its latest project – a world first – will do that reputation no harm.

“We are different to other major players in this sector as we embrace customised solutions for our customers to a greater extent,” Mark O’Toole, Business Development Manager of NEPEAN Longwall, told IM. “We are not trying to protect an inflexible supply chain, and that allows us to design the best solution for each customer.”

NEPEAN Longwall has recognised the changing market in Australia where new mine approvals are more difficult than ever, access to capital is constrained and customers are looking for cost-effective solutions to make the most of their underground reserves.

It was Centennial Coal’s Clarence mine in New South Wales and its Panel & Pillar Partial Extraction Project that gave NEPEAN Longwall the opportunity to focus on innovative mining methods using existing technologies. Centennial’s project started with concepts generated by Robert Langford (Engineering Manager, Clarence Mine), which NEPEAN Longwall turned into reality with the new system.

“There are now a number of new bord and pillar coal mining projects emerging in Australia as open-cut operations seek to access deeper reserves and head underground,” O’Toole said. “Bord and pillar operations can extract the resource quite efficiently, but this can drop off in some conditions such as lower seams.”

Longwall mines, on the other hand, rely on the complete extraction of the coal in a panel arrangement. As the panel is mined, complete subsidence or caving of the overlying rock strata occurs into the mined-out area behind the working mine face.

Pillar extraction disappeared to a large extent from Australian mines in the late 1990s due to safety concerns about the unpredictability of roof behaviour while mining. “Pillar extraction is not possible on all leases, but where it is an option, we now have a concept that provides a controlled area for safe mining,” O’Toole said.

The new concept is called the Resource Extraction System or RES for short.

This system is a hybrid between longwall technologies and bord & pillar technologies. It uses powered roof supports to control the roof in the mining area and a continuous miner to cut coal in front of the roof supports. The services to power the roof supports are able to be mounted in a centre roadway with supports laid out to the right hand and left hand. In a simple system, there may be as few as 14 roof supports used.

“In discussions with customers and geotechnical staff there is a view that, due to the narrow working face, the roof supports will never be in yield conditions and the extraction may be viewed as sub-critical – not resulting in surface subsidence,” the company said.

For coal cutting, a continuous miner and shuttle cars are employed. The continuous miner breaks away to the right and cuts in front of the roof supports for a distance of around 12 m, as it does so the canopies advance behind the cutter head and a forepole is extended towards the face. The continuous miner withdraws from the cut and the roof supports are advanced to the face. The process is then repeated on the left-hand side. In this way the system advances through the two pillars leaving behind a goaf.

In some applications the entire pillar can be removed, which has advantages for ventilation of the face; in other applications, the pillar may be partially removed, leaving a remnant.

For a capital spend which is less than a new continuous miner the mine can benefit from increased yield from the resource while maximising the value from existing production machinery, the company says.

The RES is designed to safely remove all or part of the pillar in a room & pillar environment, with operators and equipment under the protection of roof support canopies and roof supported by traditional longwall roof support methods.

The patent-protected system also provides new opportunities for providing continuity of production during longwall relocation or during discontinuities in longwall production and the ability to mine areas in mining leases previously considered high risk, the company says.

“Reflecting on the lessons from our first project, we realised that we had to think differently about the powered roof support,” O’Toole said. “This is not a longwall. The application is quite different and the method of operating the roof support is quite different. This realisation has led to us developing lighter structures with different hydraulics that are able to move quicker. With this approach the roof support will be less costly than a typical longwall unit.”

Flexibility will remain a unique selling point of this solution, yet there are some fixed requirements to consider.

As is currently envisaged, a narrow head miner is needed for the continuous miner to work effectively. Mining operations will also have to have suitable ventilation in place to support the operations. The application of RES is best suited to geologically-stable areas with the aid of roof supports with load bearing canopy forepoles and face sprags.

The flexibility comes from the modular design of the equipment, as well as the ability to tailor the system dependent on the size of the area to be extracted and the inherent geology. The services to run the roof supports, power distribution, pumps and motors, hydraulic tank, dump valve and filters are all mounted on a modular skid, which is advanced down the roadway by the system. In other applications of the system, these services may be monorail-mounted or Pantech-mounted.

Depending on the panel layout, roof supports may be added for increased width or removed for a narrower working face.

Advanced technology has been incorporated into the first project with remote operation planned from the start of production from an underground control pod. This pod, located hundreds of metres from the face, allows control of the roof supports and the continuous miner. Existing technology has been incorporated including cameras, infra-red sensors, inclinometers, transducers, Wi-Fi, flameproof screens, gas monitoring, etc. Having the operators underground allows them to double their role and perform maintenance and inspections as required, NEPEAN says.

“We have partnered with NEPEAN Conveyors to develop other applications of the concept,” O’Toole said. “Some seams will not tolerate the ‘tip to face’ requirement when a continuous miner is used, so we also have a system based around a single armed shearer and a cutting capacity of 500-800 t/h.

“It is attractive if these systems can operate as an advancing face as this eliminates costly gate road development. The panel turns out of the main headings and then starts to produce coal off the face immediately. Our current project is solving the coal clearance, ventilation and services requirements of the advancing face. It is an exciting development as the projected capital outlay is significantly less than for systems requiring a continuous miner and continuous haulage.”

He concluded: “We have been committed to the underground coal industry for the last 25 years and the addition of these systems into our portfolio allows us to cater to the changing needs of the industry over the next 25 years.”