High desert tower cranes
8 August 2019Mining has been a key feature of the Chilean economy since the earliest days. Julian Champkin finds that lifting methods have become uniquely adapted to the conditions of South America’s Southern Cone, with tower cranes operating for decades in the Atacama desert and beyond.
Tower cranes are primarily associated with construction. Leibherr in South America have developed a distinct niche for tower cranes in the mining industry. "The mining sector is one of the most developed industries here,” says Henning Kohler, head of the tower crane division of Liebherr Chile, “and tower cranes have become a useful tool.”
The mining sector is one of the mainstays of the Chilean economy: it accounts for more than one-third of government income. Copper is primary, coming mainly from the Norte Grande region, which includes the Atacama Desert, where conditions are particularly extreme. Temperatures and wind speeds are high, and the Atacama is known as one of the driest regions on earth, with some weather stations never having recorded rain.
Peru, adjoining to the north, has similar geology and extraction methods. Local practice in both countries is for large, generally open-cast, mines to break up their ores in crushers, then to treat them with chemicals in large tanks, called flotation cells. “The result resembles a brown sludge,” says Kohler, “which is churned by powerful motors until the desired product is dissolved out.”
The motors, weighing up to 50t, need servicing every two to three weeks. They are lifted out of their cells onto lorries, and taken to a warehouse for maintenance and refurbishment. Practice elsewhere would be to use gantry cranes for the task. “We have all but eliminated gantry cranes from mining in Chile and Peru,” says Kohler.
Instead, tower cranes are brought to new mining sites to construct the facilities. So far, so standard. “But then they stay on at the site. They remain for the next twenty or thirty years, and are used for that regular lifting and replacement of flotation cell motors.”
There are two main reasons for this niche use of tower cranes. One is geographical. “Many of these plants are in very remote and hard-to-reach locations. Having transported a tower crane to these places, it makes little sense to take it away again and replace it with a gantry.”
The other is geological: “The western coast of South America is seismically active. We are an earthquake zone,” he says.
Curiously, and counterintuitively, tower cranes withstand earthquakes very well, and do so better than gantries. “In an earthquake the mast of the tower crane flexes back and forth, almost like a whip,” says Kohler. “The flexing absorbs the kinetic energy of the earthquake and dissipates it.” It is the difference between a reed and an oak tree in a storm: the reed bends and is unharmed, the tree breaks. He has evidence to back the theory: “In 2010 a large earthquake struck at 3.00am on a Saturday morning. No Liebherrs came down, and no-one was hurt.”
This use of tower cranes began in 2009, and is continuing strongly. Liebherr is at present involved in more than 15 mining projects in Chile and Peru. “We are just sending a 1250 HC 50 tower crane to Southern Peru, to the Quellaveco mine, some 3,700m high in the Andes,” says Kohler. “It has 50t maximum load and a tip load of 12t at 81m radius. It is by far the largest tower crane in Peru. We normally enter three-year renewable maintenance contracts for mine cranes. We expect this one to be maintaining flotation cells for the next 30 years.
“We have sold another 1250HC, to the Quebrada Blanca mining project in Chile.” Both are scheduled for erection at the end of August 2019.
Liebherr has also just finished the commissioning of a 630ECH 50 Litronic Tower Crane in a copper mine in the Atacama. Again the work is on flotation cell maintenance, with a two decade life span envisioned; the crane has 50t maximum load capacity, with a 7t tip load at its maximum working radius of 73.4m. It is mounted with 41.2m height under hook.
South American countries also use tower cranes more conventionally. “We have an ambition to set up a rental fleet of 180 Leibherr tower cranes in Columbia. There the need is for construction,” he says. Liebherr have supplied tower cranes to some 15 mining projects in the region, as well as harbour cranes and mobiles throughout South America.
