By 2003, if all goes to plan, RAG American Coal Company will install the widest longwall face in the USA at one of its operating mines. Though exactly how wide the longwall face will be is still under close investigation, according to Klaus-Dieter Beck, RAG American vice president planning.
New longwall equipment for the mine is due to be purchased in 2002, to begin operating at the start of 2003. While Beck said the optimum face width was yet to be determined, current indications are that it could be between 450m to 500m. At present, the widest face in the world is believed to be a 500m wide face at Warndt/Luisenthal mine at the Saar region in Germany. Beck said given current levels of technology the limits in face width have probably been reached but new technology expected to be available next year which will make longwall face widths of up to 600m feasible.
The technology step-change that must be realized to make faces wider will include the implementation of the variable frequency motor technology. “We are talking about 1400 to 1800 hp motors for 4160 Volt power systems, gearboxes of the class 65 (650.000 Nm), face conveyor chain diameters of 48 mm probably 52 mm," Beck said.
Apart from these mechanical issues, other design challenges in getting faces to these lengths have included the soft start of a face conveyor, face ventilations and dust control, Beck said.
"Everything with respect to the drive systems had to stay in a small size to complement gate development and transportation. New electronic equipment made it possible to reduce the size of the electrical parts and new metallurgical technology made it possible to design stronger gearboxes of the same size as old ones."
Operational difficulties in implementing faces of this width are not expected to be more difficult than the introduction of any new technology.
On the current status of the RAG American project Beck said: “We are still assessing different options including basic studies about friction numbers of the conveyor and monitoring precisely the performance of the current drive system technology.”
Significant new equipment being purchased to support the extension include new gearboxes, new chains, soft start technology for drives and VFD technology. Not surprisingly, the mine plan has undergone significant change. Beck said part of the ongoing investigation was to examine the impact of the wider face on subsidence issues, rock mechanics and roof control, dust and ventilation.
Beck said advantages were drastically reduced costs for development of the longwall panels: “The costs for producing coal from the development sections are almost twice as high as from longwall production. So the saving effect by reducing the amount of coal from development section is high. An additional effect is the increased float time for the new longwall panel. RAG has always been a leading company in driving longwall technology and this is just another example as evolution improves safety, health and productivity.”