Column: Zinc concentrates squeeze but there’s no shortage of metal
Global zinc mine production continues to slide and the raw materials squeeze is now starting to bite, particularly in China.
Kotinskaya, Russia’s most productive underground coal mine, has won an additional benefit from its record-breaking longwall face equipment, based around Cat® roof supports and armored face conveyors. Caterpillar tested a shield from the mine at its manufacturing facility in Lünen, Germany, and the results showed that the roof support condition justifies an additional 20,000-cycle life extension—with no major rebuild.
Operated by the Siberian Coal Energy Company (SUEK), Russia’s largest individual coal producer with an output of 97.5 million tonnes (Mt) in 2012, Kotinskaya mines thermal coal from the Sokolovskoe coalfield within the Kemerovo region of western Siberia. Over the past eight years, its longwall face has repeatedly raised the bar by achieving new production records at regular intervals. In 2006, Kotinskaya broke the 4 Mt barrier for the first time in Russian mining history. Since then it has pushed the record to more than 4.7 Mt annually from its single longwall installation.
Kotinskaya’s longwall is equipped with 1.75-meter-wide, two-leg Cat shields that have support capacity of 725 tonnes each. With an operating range of 2,200 to 4,800 mm, the supports are used in a seam that is typically more than 4 meters thick, on face panels that are 230 to 250 meters long. A Caterpillar PF 4/1132 armored face conveyor (AFC) completes the longwall support and transport package.
While the face equipment for Kotinskaya was delivered in 1998, mine development delays meant that the shields and the AFC were not actually put into operation until 2004. Stored outside during the six-year wait, the shields were commissioned successfully without the need for any extra maintenance. Since then the shields have run through their 30,000-cycle design lifespan. To date, the mine’s successive longwall panels have produced more than 28 Mt of coal while achieving an impressive series of output records, including 702,000 tonnes of coal cut in a single month.
Comprehensive roof support testing
Last year, SUEK returned one of Kotinskaya’s original roof supports to Caterpillar for testing. Caterpillar’s comprehensive test facilities at Lünen include three shield test rigs that can provide a force resistance of up to 20,000 kN and a test height of more than 5.0 meters. Used together with leg and cylinder test machines and hydraulic test rigs, technicians tested the structural, hydraulic and control components.
Once a 30,000 cycle test run had been completed at 10% overload, Caterpillar was able to report that the shield had performed as intended during its design life and that the face equipment at the mine should be good for another 20,000 cycles without the need for any major rebuilding. The tests also show that with only minor rebuild work, the shields will carry on for another 10,000 cycles beyond that—effectively doubling their lifespan at minimal extra cost to Kotinskaya.
To date, the only significant alteration that has been made to Kotinskaya’s shields has been an upgrade from the original Cat PM4 pilot controls to a state-of-the-art Cat PMC-R® electrohydraulic control system, which enables the shields to be operated automatically. In a mine where roof supports experience shock bump loading, Cat roof supports have shown the ability to double their design lifespan while contributing to record production levels.
