Published in the August 2007 American Longwall Magazine
Pennsylvania-based John T. Boyd discussed longwall trends at June's Longwall USA event in Pittsburgh, Pennsylvania, reviewing recent figures in US production while looking ahead to 2007 through to 2012.
While the longwall mining method enjoyed a heyday in the 1970s, about a decade after its introduction in the US, the number of longwall faces and longwall mines has steadily dropped. In fact, recent drops in output can be linked to the face closures at some mines which were previously known to be highly productive, such as West Virginia's Aracoma, Alabama's Jim Walter Resources No. 5 and Utah's Crandall Canyon.
The five main production regions - Northern Appalachia, Central Appalachia, Alabama, the Midwest and the western US - were all broken down by the Boyd researchers with a snapshot of 2000 to 2006 offered. With some areas seeing production cut in half during that time (such as Alabama, which has dropped from 16Mt to 9Mt during the period), the only area seemingly exempt from the downward trend is the western US (45Mt in 2000 to 56Mt in 2006).
As of the US summer of 2007, 49 active longwall faces could be accounted for throughout the nation.
Boyd experts noted that there was a period of time during the 1980s and 1990s when longwall output paralleled production by continuous miner; however, especially since 2000, this is no longer true.
One interesting factor observed, said Boyd, was a downward shift in labor force numbers - simultaneous with production upswings. There are a few reasons for that, and for overall upped output from US mines, including improvements on equipment, increased panel sizes, higher capacity belts, and a jump in shield width and cut depth.
In short, it said, the industry is doing more with less manpower thanks to ever-changing longwall technology. Panel lengths of 600ft to 5000ft in the mid-1980s, for example, are now an average of 1000ft to 11,000ft.
Boyd also evaluated tons produced per man-hour at eastern mines versus western mines in the US, and found that both are on their way down. It cited issues such as infrastructure constraints, maturing mines, a slowed pace of new face installations, and the skills gap and workforce turnover suffered at many mines for the declination.
Meanwhile, each man and woman who takes a mantrip or truck to an active section each day is doing it more safely, the consultant reported. The industry has seen a 60% drop in lost-time accidents since 1988.
The past must be studied in order to provide an accurate portrait of the future, and Boyd did just that. While underground mining has dipped slightly to an estimated 354Mt in 2006 from 366Mt in 2004, Boyd predicts a turnaround for the sector that could bring totals to 391Mt by 2012.
Continuous mining, while up slightly, will see a downward trend, the researchers said. With 174Mt of production in 2004 up to an estimated 179Mt last year, Boyd's prediction for the sector by 2012 is 163Mt. However, longwall production is currently down - from 192Mt in 2004 to last year's estimate of 175Mt - and new installations will help bring it around to a projected 228Mt in five years time.
The ever-changing face, literally, of longwalls is a factor that must always be considered. New operations are under development throughout the US, but others are beginning their closure processes as they become completely mined out. By 2012, the total number of longwalls in the country should be about 53, Boyd researchers predicted.
While a mixed bag of news - most significantly the flatness forecast for longwall mining despite operational efficiency increases - economic factors for new mines are promising. The average seam thickness for a single longwall face is estimated at 6ft with a projected annual output of 6.5Mt. Two decades is the estimated average for the life span of new mines, the researchers said, and the mean employee count of 435 should be able to produce about 6t per man-hour.
Click on the tables on the right to see detailed statistics.
