High performance longwalling 'down under'

Staff Reporter

Delegates at an international conference in Germany were told that the key to improving the performance of Australia's high performance longwalls lies in improved equipment utilisation and effective maintenance schemes. Speaker, Brian Nicholls, a consultant and general manager of the central Queensland North Goonyella mine, was giving the 300-strong audience an overview of the history and evolution of longwalling in Australia.


The Second International Symposium "High Performance Longwall Operations," was held at the Aachen University of Technology from 13-14 June.


Those who know Nicholls will recognise themes that dominate his operating style. Nicholls has consistently argued that high performance longwalls do not need more capital investment (he recently bought a second-hand Joy shearer for North Goonyella). The focus should be on improving utilisation and "systematic component changeouts prior to failure,... [which] add up to increased production capabilities."


Nicholls said the quantum leap of the last ten years in equipment size and capabilities had made it possible to mine thick seams of 3.5-4.5m in the Bowen Basin. Bigger equipment at some newer operations included +30t supports rated 1,000t/supports and AFC capacities exceed 5,000 t/hr, with AFC driveheads weighing in excess of 40t. Newer shearers can weigh over 80t with installed power of over 1,600 kw.


This had seen the development of operations such as North Goonyella, Newlands, Moranbah and Oaky North. Many of the high performance faces were only reaching their production potential for short periods, however. MIM's Oaky North was out of action for about 8 months after being buried. North Goonyella lost 13 weeks in the last six months but was still able to produce 3 Mt in the fiscal year to May. Moranbah North has struggled with coal clearance problems since early in the year.


"The objective over the next decade has to be improving reliability through engineering design, simplifying component changeouts and the associated handling systems with more effective face management on a consistent basis," Nicholls said.


While production performances of longwalls extracting medium to thick (3.5-6m) seams is exceeding 10,000 t/shift, Nicholls warned of the dangers inherent in much bigger equipment.


"Performances of these dimensions are introducing other problems to the operators related to equipment size, required development rates, coal handling, conveying and underground environmental issues with dust and gas make control."


Some major problems were transportation of heavy face equipment (design of equipment handling machines, floor pressures, etc.); longwall roof conditions (height of working environment, hard and soft rocks, face and rib spalling, etc.); and handling of equipment components (support legs, DA rams, AFC chain links, etc.)


"All these problems are magnified many times as extraction height and equipment size requirements are increased to meet the drive for greater production rates and reduced costs. Operators using this large high capacity equipment, who fail to seriously consider the implications of dealing with associated problems, can pay severe penalties by way of lost production when things go wrong... Some AFC problems with 42mm and 48mm chains and in excess of 1,700 kw drives can also take days to fix... On the positive side, well-managed, high capacity faces can produce large volumes at high productivities and low cost."


Speaking at the same conference, Frank Leschhorn, general manager RAG Australia, said he believed that geological constraints would be a critical factor controlling longwall performance. Leschhorn said there are cases where hundreds of millions of dollars were spent on longwall equipment and infrastructure in spite of a huge lack of knowledge of the deposit.


Leschhorn highlighted the problem of keeping development ahead of face retreat with increasing rates of extraction and extended panel-length.


"The installation of longer faces should not be the solution for the development misery of many mines in Australia," Leschhorn said. "Better performance is needed to match the future challenges by changing to three entries at some mines, when they become deeper and have to solve increasing methane and ventilation problems."


Leschhorn said in cases where geological conditions do not allow wide unbolted areas or the pillar length becomes too long for flitting the continuous miner, high-performance integrated systems should be used, and in special cases one unit in every entry.


"There are already good signs for improvements in Australia: e.g. at MIM`s Newlands mine in Queensland a single Joy 12/12 CM with a 15 t shuttle car drives an average of 600 m/week with peaks of more than 100 m per shift."


Looking to the future, Leschhorn, predicted that competition between the low cost opencut thermal coal producers in Indonesia, South America, South Africa, Australia and China would affect the future of longwall mines in Australia and North America.


"In the coking coal sector the Australian home competition between the older opencut mines and the very new high productive longwall operations will become crucial, because the market expansion will not support them all."

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