Published in the August 2006 American Longwall Magazine
“Among the world’s largest coal producers, most notably the US and China, longwall mining increasingly is becoming a game of inches. In helping coal mine operators, Joy Mining Machinery is well ahead among the world’s longwall equipment manufacturers,” says Joy engineering director for shearers Ed Niederriter.
Long thought the domain of plows, two recent engineering breakthroughs at Joy now make it possible for longwall operators to apply the advantages of conventionally designed shearers in seams not previously possible.
According to Niederriter, the shearer holds many advantages in mining low seams.
“The four most significant advantages are the shearer’s ability to mine hard material that intrudes into the seam, their ability to follow the seam, especially with soft bottom or top, their ability to vary the extraction height ‘on the fly’ and the fact that shearers do not require that the conveyor drive sit in the tail entry.”
Bringing these advantages to lower seams of coal has been made possible with the development by Joy of a new shearer downdrive design and the Joy Broadband Low Profile Chain armored face conveyor (AFC).
Together, they have trimmed more than five inches – 5.25in – from the minimum height requirement for Joy’s low-seam longwall mining system. “And, in a game of inches, five inches is more than measurable, it is considerable,” Niederriter said.
“In addition,” he continued, “not only does the operator benefit from the inherent advantages of the shearer machine, the machine itself brings with it the benefits of Joy’s Optidrive system.”
With Optidrive, all Joy machines – the shearer, the continuous miner, the shuttle car and the Flexible Conveyor Train (FCT) – share common drive components and parts, with the same part numbers. This allows the mine operator to reduce his inventory and improve his maintenance, as what is learned on one piece of equipment is applicable to all pieces of Joy equipment. What makes Optidrive unique to each piece of mining equipment is the software that controls the individual systems.
Combining the power and versatility of Optidrive and the advantages of plows opens new possibilities as the world’s leading producers look to lower and lower reserves, Niederriter said.
“The reason for this increasing interest in lower seam coal is that coal operations find themselves with fewer options for medium-seam longwall mining and the industry is forced to mine at lower heights, most notably in the United States where longwall panels increasingly are under five feet high, and in China where national policy dictates that their thinner overlaying seams of coal be mined before the higher lower seams,” he said.
Niederriter noted that, as challenging as the low-seam mining environment can be, it is an inevitability the industry must face. “In recent years, lower-seam longwall mining has become increasingly necessary, but it’s the mine’s perspective on that seam’s potential that is the key to keeping productivity up.
“As a result, there have been a couple of gradual shifts that have been occurring in longwall mining in the past two decades in the United States. In particular, the number of longwalls has decreased from 92 to 52 in the last 17 years and, at the same time, the range of mining heights has narrowed somewhat.
“In a prior time period, there were 12 longwalls operating in less than 5ft; five with plows and seven with shearers. Presently, there is just one plow longwall in the US and there are no shearer faces operating in less than 5ft not due to a lack of interest but rather due to a lack of appropriate mining equipment. Until now,” Niederriter said.
“Several factors have brought about this change.
Among these, a major issue was operating cost since lower longwalls tend to be less productive and therefore more costly to operate. As the realized price of coal declined in the previous time period, these ventures simply were not economically viable.
“Another factor in recent years that has prevented the pursuit of the lower seams is that increasingly more robust equipment has become the standard in longwall mining. As operators demanded more powerful and longer lasting shearers and AFCs, the machines became taller and less suited to the thinner seams,” he said.
“In today’s world, longwall reserves in the US Appalachian coal fields above 5.4ft have become increasingly harder to find, with the result that there is a cluster of about 20 longwalls mining in the range of 5.4-6ft.
“Because this range is outside the existing seams, many of these operations are forced to mine an increasingly large percentage of dirt and rock in order to extract the coal. There is little doubt that most, if not all, of these operators would mine lower if suitable equipment were available.”
He said it was the realization by Joy that as available reserves become thinner, the necessity for equipment to mine these seams efficiently led the company to develop the new downdrive design that meets both the demand for lower operating height shearers and the mine operators’ expectation that they will deliver the demanded production levels.
According to Niederriter, Joy’s new downdrive system allows the 7LS and 4LS shearers to be lowered on its popular Ultratrac 2000 haulage system, bringing the body of the machine an additional 3.2in closer to the AFC.
Complementing the reduced height of the shearer machine was the development of the Joy Broadband Low Profile Chain AFC Pan. The Broadband Low Profile Chain’s main feature was that it preserved a 42mm chain strength while lowering the sigma 1.26in. At the same time, with the lower profile, the AFC rack mountings are lowered, resulting in an additional .79in reduction in height.
With this combined shaving of 5.25in off the minimum required on the Joy low seam longwall mining system, the 7LS and 4LS shearers now can operate in seams as low as 59in.
“The Broadband Low Profile Chain has a 100% improvement in the link contact area over other available chains that don’t have the height advantage and a...click here to read on.
