This unorthodox strategy was recently put to the test when Murray Energy committed to use this equipment development philosophy to design and manufacture several new high-production longwall systems for the Century, Ohio Valley and New Era mines. Longwall panels at these mines were being developed with 1,150- to 1,630-ft face widths and panel lengths up to 12,000 ft. To meet the challenge of moving this much coal, Murray Energy’s team established aggressive equipment expectations for its armored face conveyor (AFC) drives. The drive technology needed to balance the requirement of providing high break-away torque for heavily loaded chain conditions, as well as protect the chain and drive components from anticipated shock loads resulting from sudden chain jams.
One of the key requirements was that the system must be simple to control, while easy to operate and maintain by the mine’s longwall and maintenance teams. This approach insured that Murray Energy did not have to rely on outside services to provide critical support when problems developed that could potentially result in unplanned downtime. Based on the preliminary engineering work, the company decided to use 3 x 1,960-hp drives for all of its new high-capacity AFC systems. This represented the highest power for AFC drives currently operating in the U.S.

Transferring all of this power to the chain in a controlled manner required an advanced, well-proven technical solution. Murray Energy contacted RM Wilson Co., which supplies high-quality products and rebuild service support for AFC drive systems. When given the opportunity to provide input, RM Wilson recommended Voith Turbo’s high-power range fill controlled fluid couplings. These actively controlled and actively cooled couplings were specifically developed for high-powered AFC drives.

RM Wilson had previously supplied Murray Energy’s mines with Voith’s constant fill couplings for AFC drives up to 3 x 1,000-hp, however, the jump to 3 x 1,960-hp exceeded the thermal range of constant fill fluid couplings. RM Wilson was aware that Voith’s fill controlled fluid couplings were already a well-proven solution and it organized a meeting with Voith to further discuss the control system requirements. Voith presented the newly developed automated cooling circuit (ACC) control scheme, which greatly simplified the hydraulic control components and resulted in the lowest possible water consumption for the drives. Based on the simplicity of the ACC control scheme, Murray Energy’s development team was satisfied that integrating the coupling control function into its longwall controller would be a straightforward process.
Meeting the demands of these high-powered AFC systems required detailed examination of the performance requirements of each major component of the drive. RM Wilson facilitated the coordination of various technical meetings with prospective drive component manufacturers and the Murray Energy Longwall Development team. The result was a properly engineered drive solution where the motor, fluid coupling, gearbox, torque limiting coupling, and chain were matched to the system performance specifications.

Installation & Commissioning
Murray Energy is currently operating these new high-capacity longwall systems at the Century, Powhatan No. 6 and New Era mines. The company also plans to install a similar system at its New Future mine during 2014. The longwall was initially commissioned (September 4, 2011) at the Century mine, which now has the longest history of operation on the new system.
The first Century installation was a relatively short longwall panel. This provided an opportunity to give the new system a thorough test and work out any technical issues. Considering the challenge that was accepted with this unusual approach to designing a large engineered system, the new longwall started producing coal in spite of some minor technical issues that arose during initial commissioning. Surprisingly, the mine was able to produce coal as they worked through these technical issues. This feat was partially attributed to the forgiving nature of the drive technology chosen for these systems, which confirmed Murray Energy’s requirement that the system be simple, yet robust and reliable.

The second longwall system installation began operation on September 25, 2011, at Murray Energy’s Powhatan No. 6 mine. The third system was installed at the New Era mine on June 6, 2012.

The Century mine has successfully completed six longwall panel moves with this new equipment and they are now mining a 12,761-ft long and 1,482-ft wide panel. The system has been performing well and is now consistently producing more than 800,000 tons per month. The Century longwall recently achieved a company production record of more than 1.1 million tons in a single month.

Murray Energy has every expectation that these longwall systems will prove to be among the highest producing longwall systems in the U.S., with the potential to exceed 8 million tons per year from a single longwall mining operation.

The system availability is high and they have not experienced any chain failures, in spite of the fact that the 48-mm chain can, under high-load starting conditions, experience tensions levels that approach the approved load limits. To date, the Murray Energy mines have noticed a considerable increase in chain life attributed to the very soft starting behavior of the Voith couplings (25- to 40-second start time). The controlled application of torque, along with the torsional dampening characteristics of the fill controlled fluid couplings mean that users can expect the maximum possible life out of all drive components and AFC chain.

Despite the already observed increase in equipment life, the drive components get a thorough inspection and rebuild after each longwall panel.

James McClenathan is vice president-technical services for RM Wilson Co., located in Wheeling, W.Va., and Roland Hoet is director of mining and metals for Voith Turbo, located in York, Pa.