Yesterday the Boards of Directors and senior management of Cliffs Natural Resources and Bucyrus International, world leader in plow technology, co-hosted an event to celebrate the delivery of the first modern automated plow system in the US with a ceremonial unveiling at the Bucyrus facility in Houston, Pennsylvania. Guests were given the opportunity to view the longwall plow system up close above ground before it is installed in Cliffs’ Pinnacle coal mine near Pineville, West Virginia. The host companies gave presentations on plow longwalls as the preferred method for medium and low seams below 1.8 m. The benefits of a high level of automation were also covered.
The presentations were followed by a live operating demonstration of the system. For Cliffs, the unveiling marks the start of a new era in low-seam productivity and safety. For Bucyrus, it marks the kick-off for a nationwide promotion of this highly advanced and efficient technology, “which is ready to assume the important role in North American mining it deserves,” the company says. “Despite the fact that Bucyrus automated plows are in service around the world, North America has been reticent to embrace this technology. This reluctance has been based on a performance perception dating back to the 1970s when plow systems were not automated and did not possess the cutting and conveying power of today’s systems. But after exhaustive research into the most efficient mining method for low seam coal, Cliffs decided to opt for an automated Bucyrus plow longwall as the safest, most cost-effective and most environmentally friendly way to extract coal from low seams.
“Shearers can operate in seams of 1.5 to 6.0 m, but are considered less than optimal in seams of less than 2.3 m. Plows can operate in seam thicknesses down to 0.6 m and up to 2.3 m. Bucyrus automated plow systems are used worldwide in underground coal mining. The plows are operated in China, Czech Republic, Germany, Kazakhstan, US, Mexico, Poland, Ukraine, and Russia.”
The plow was invented and refined by Wilhelm Löbbe, chief engineer at Westfalia Luenen (a predecessor company of Bucyrus Europe), back in 1937 in an attempt to modernise and mechanise underground coal mining. This was later followed by the ‘fast plow’, which achieved daily output of over 1,000 t for the first time in 1950. Since then, Bucyrus has re-invented the plowing technology by adding numerous new features – including incremental (defined cut) plowing and horizon control – as well as boosting installed power to allow faster extraction. In contrast to a shearer, which requires considerable height to operate, the very compact plow can operate in seams as low as 0.6 m. This allows extraction of coal seams previously thought to be unworkable. For any seam under 1.8 m, the plow is generally the better proposition. Also, the plow has no problems with coal flow which is in front of the plow – as opposed to the shearer, where the machine body at times needs to pass over the coal flow creating a restriction to material conveying capacity. But even more important: the shearer operator has to travel with the shearer through the face to control it. In low seams this presents challenges to the operators in terms of what they are physically able to accomplish during any given production shift.
Today the Bucyrus automated plow systems represent a reliable and well-engineered cutting technology. With installed power of up to 2 x 800 kW and traveling at up to 3.6 m/s, Bucyrus plows extract coal at rates of up to 3,500 t/h.
In contrast to shearers, which always require an operators presence, automated plow longwalls do not require operators to be located in the production face, resulting in a much higher level of operator safety.
Conventional plows typically only allow the plow ‘pushing’ pressure to be set – not the cutting depth – with the result that the cutting depth varies with coal hardness. Bucyrus incremental plowing, which is precisely controlled electronically, ensures that the plow cuts to an exactly defined depth, regardless of coal hardness, seam structure and presence of rock intrusions. This results in balanced loads on conveying equipment and a steady advance of the longwall through the seam.
The plow can negotiate seam undulations much more easily than a shearer. This allows selective cutting of coal without adjacent strata, reducing wear and tear on equipment and cutting energy demand as well as coal preparation and mine waste disposal costs. Seams often rise or fall both laterally and in the direction of advance. Bucyrus horizon control ensures that the plow does not dig or climb unless required by the seam geology. This excellent control also allows mining of seams with a face or uphill panel inclination of up to 45° and a downhill panel inclination of 20°, as compared to 20° for all inclinations for a shearer.
With thick-seam coal reserves dwindling worldwide, it is important that thin- and medium-seam coal is not lost through ‘sterilisation’ caused by mining underlying thick seams first. Plows allow the overlying thinner coal seams to be mined first, ensuring that valuable coal is not buried forever. Plowing also offers higher recovery rates than Room & Pillar mining, as no pillars need to be left behind in order to support the roof. It also expands the magnitude of reserves by adding those which were previously considered not to be recoverable based on safety or economic reasons.