Rock and ore: Mining's specialist lifting equipment9 August 2023
Mining is a specialised business that requires specialised lifting equipment. Julian Champkin reports.
Mining is more than dark underground tunnels of men with picks and machines extracting coal – vast opencast pits from which giant bucket excavators load tonnes of rock and ore are mines as well. So too are strip mines, where the overburden is removed and the wanted material is accessed from the surface. There is also placer mining, which is essentially sifting riverbed sands for, typically, gold or gemstones that have been washed down from their original sites by centuries or millennia of water erosion. All of these methods of extracting things we want or need from the ground come under the heading of ‘mining’, and all of them need different kinds of lifting equipment. And these days almost all of them are carried out at extremes of scale, quantity or depth that strain technological ingenuity to its limits.
Most unusual perhaps is the offshore dredging for diamonds from the ocean bed, practiced off the coast of Namibia. There are also new uses for existing or redundant mines – which again need specialised hoists of custom designs. More standard in concept, but impressively large is the Sishanling iron ore mine in China – 30 million tonnes a year is the planned extraction rate. This is a new project, which Hoist first reported on last year (April 2022). Since then, rapid progress has been made.
Siemag Tecberg is the hoisting firm involved. The installation of the rope sheaves and of all three hoists has now been completed and some of them have been put into operation: the two Koepe (or friction winding) hoisting machines – one four-rope, one six-rope – of the service shaft are already working. No-load commissioning was completed for the production shaft’s six-rope Koepe machine; rope-up started in mid-March this year. Due to slow construction progress in the area of the main shaft loading and unloading station, the commissioning of this hoist is scheduled for October 2023.
At present, Siemag Tecberg is on site with preparatory tasks for the commissioning of the main shaft. Once the ropes for the production machine have been laid, the installation and connection of the shaft switches and the connection of external equipment, such as the loading and unloading stations, will be carried out, with safety tests. Finally, commissioning of the production machine under load takes place, together with tests of the control system and final optimisation of the parameters of the drive and braking systems.
DIGGING FOR DIAMONDS
Southern Africa is, of course, another world centre of mining, and Condra, based in Johannesburg, has been a major supplier of lifting equipment since 1971. In March this year it announced a contract to manufacture a 15-ton suspension crane of an unusual configuration. It is for use underground at a Botswana diamond mine, and is one of two overhead cranes ordered. The second machine is of conventional overhead design.
The arrangement of the first suspension crane is one rarely seen: two I-beams defining its area of movement will be bolted to rock-bolt flanges anchored in the roof of a mine chamber that will have been blasted and excavated. I-beams are usually the topmost side components of a fixed gantry that has been constructed from the ground up. In this case, however, they will hang from the chamber’s ceiling. The wheeled 11m-span crane girders will then run suspended from the lower flanges of these two long-travel I-beams, with the crane’s crab mounted atop of the girders to provide the cross-travel. The whole structure of the crane becomes suspended, running along and across the roof of the chamber.
Condra designed this crane to specifications supplied by the project’s consulting engineers. By suspending the crane, it will deliver the greatest possible lifting height, reducing the volume of rock needing to be blasted and excavated to form the chamber. After installation, the 11m span, 15-ton crane will have a lifting height of 9m. Condra has previously manufactured similar suspension cranes for mines in central Africa.
The second, more conventional, overhead crane for the diamond mine will have a 35-ton capacity and 9.2m span and will work in a larger existing chamber. Lifting height will be 12.7m.
Remoteness, in terms of distance and of poor access roads, is a feature of many of Africa’s mines. Condra is accustomed to designing for the problem, as another recent contact showed. The order, from Consulmet, was for a mine in Angola: an overhead crane and gantry were required specifically designed to overcome constraints in delivery and functionality.
Condra’s customised proposal for a product designed and manufactured in South Africa won through against tenders submitted by several rival firms headquartered elsewhere.
There were two challenges. First, the mine needed to be able to position the crane over three milling and screening areas, which are to be constructed in phases, and serviced by multiple conveyors on either side. Second, the nature of access roads to the site dictated that it must be possible for the 28m-span crane to be disassembled into 12m containers.
Unsuccessful tenders put forward a variety of designs based on portal crane configurations, which would have been limited to serving the first mill area only. They would have been unable to service future units because of conveyors interrupting the portal rail route.
Condra’s solution instead proposed a double-girder overhead crane running along an extendable crane gantry. The gantry will be erected initially over just the first milling area, with its legs sited between the conveyors to allow uninterrupted crane movement over them. The gantry will later be extended to allow the crane to service the additional milling areas as and when they are built.
The road transport limitations were overcome by reducing the gantry leg height to match the 12m length of the flatbed transports, and by designing the 26m-long overhead crane girders to be spliced in two places so that they too would fit within the 12m constraint. Each 26m box girder will be delivered in three sections manufactured with built-in camber, then spliced on site ahead of installation. At the splices, steel plates welded to the four inside faces of the male section will deliver a friction grip to reinforce girder strength and integrity beyond that delivered by the splice bolts alone. Bolt holes will be reamed and the bolts themselves machined for an exact fit that will retain camber after assembly.
Since the legs have been shortened, additional gantry height for the competed crane will be achieved by concrete plinths cast as part of the milling area foundation, and by steel pedestals incorporating the crane’s end-carriages fastened below the crane girders. The effective lifting height after commissioning will be 16m, and the capacity is 50t. The crane is a scaled-down replica of an 80-ton machine installed at a Rustenburg, South Africa, mine. It will first assist with milling area construction before its role moves to plant maintenance.
“This proves once again that a bespoke, designed-for-purpose approach to the customer’s requirements will usually carry the day,” says Condra’s managing director, Marc Kleiner.
“It would have saved the customer money to manufacture girders integrally, but road routes to some African mines continue to present obstacles to the steerable dollies needed for delivery. In this case, no crane component will exceed the stipulated 12m load length of the five semi-trailer trucks that will carry everything to site.”
To be operated in the open air, the crane’s box girders are sufficiently large to need Condra’s patented storm brakes against wind loading. Anemometers will activate these safety devices in two stages, first sounding a siren at a wind speed of 50km/h, then automatically engaging the storm brakes at a wind speed of 70km/h, overriding crane operation and securing the machines against further movement.
Weather covers will protect all motors, and the crane will feature frequency drives throughout. Crane control will be by radio remote with pendant back-up. Delivery was scheduled for the end of June.
Mining does not stop when the ore reaches the surface. Separation and refining needs to be done, generally at the same site.
Hence the orders placed with Kuenz in July last year for two automated tankhouse cranes for a 900 kilotonnes per annum (ktpa) captive copper smelter project in Sumbawa Island, Indonesia. The order is from Chinese company NFC, the main contractor for the facilities, with Nerin Engineering as the technology provider. The mine operator is AMIN. The mine is Indonesia’s second-largest copper mine – the transition to green energy is already boosting world demand for copper as an essential for electrical components. In the geology of this region gold is a by-product of copper production, which makes the mine also the second-largest producer of gold in Indonesia.
Kuenz has developed special automated overhead travelling cranes for electrolysis plants such as this – they handle cathodes and anodes for the production of copper, zinc and nickel.
Electrolysis cranes automatically carry out the process-related sequences that are needed. They grasp and lift dozens of electrodes at once, from a large number of cells filled with electrolyte, some of which are live, and bring them to a machine area of the electrolysis plant for further processing. Afterwards, the crane returns the empty cathodes and cleaned or replaced anodes to the respective cell with pinpoint accuracy. This is a recurring, automated, programme-controlled process specific to the crane. The high precision that is needed for capturing and positioning the electrodes is given by the crane management system (CMS) developed inhouse by Kuenz. Anodes and cathodes can be placed in a cell with millimetre precision.
For safe operation multiple fused electrical insulation of the components from the building, or a redundant, backup crane control system, are fitted. A swivelling collection tray integrated into the crane collects process-related dripping electrolyte or fragments of broken anodes.
Acid-resistant steels and plastics, and special coatings, are used as corrosion protection, and components are made from duplex stainless steels.
On customer request, components can also be made from super duplex steels. Mechanical components are electrically insulated from each other with special, acid-resistant plastics, with isolating transformers used for the electrical network. The hydraulics and, if necessary, the spraying devices for cleaning the electrical contacts on the cells, are also electrically insulated. For safety reasons, the electrical insulation precautions are monitored by insulation measuring devices as standard.
Thermal cameras installed on the crane monitor the electrolysis process to detect impending short circuits between cathodes and anodes at an early stage and thus improve the overall efficiency of the electrolysis plant.
A WORLD FIRST
Once ores have been refined to metals, the product needs to be transported. In 2022, Terminal Graneles del Norte (TGN) in the city of Mejillones, Chile, ordered three rail-mounted gantry cranes (RMGs) from Konecranes.These will be the first Konecranes RMGs ever delivered to South America. RMGs are not normally associated with mining, but, in another world first, these are to handle copper concentrate from a mine, in an intermodal terminal.
Alfredo Ramirez, regional sales manager Americas, Konecranes Port Solutions, says: “This is one of the most interesting RMG cases I’ve ever worked on. These cranes will work in a special intermodal operation serving trucks and trains arriving from one of the largest copper mines in the world. They will handle special containers that carry copper concentrate – offloading full containers from trains and trucks, and loading them with empty containers”.
The cranes are heavily automated, and, taken as a whole, the intermodal operation will be automated as a single integrated system. The three Konecranes RMG cranes will be the workhorses of the system, with a lifting height of 15m and a rail span of 47m. They will have special revolving spreaders that will be used to discharge the copper concentrate to hoppers. Gantry Collision Prevention, Auto-truck Guiding and Truck Lift Prevention will be fitted. Container stacking, including discharging into the hoppers, will also be fully automated. Lifting and landing onto trucks and train wagons will be done by a human operator in a remote operating station.
Mining is varied. So are its cranes.
Lowering nuclear waste
Mines become exhausted of their ores. They can still be of use, repurposed, and may need new or updated lifting gear. Siemag Tecberg has recently installed a two-rope Koepe (friction winding) hoisting machine in the northern hoisting section of a former iron ore mine. The mine is being re-purposed for the storage of nuclear waste.
The Konrad 1 mine in Salzgitter, Lower Saxony, is the first repository for low-grade and intermediate-level radioactive waste to be licenced in Germany. Commissioning of the repository is scheduled for 2027, when the placement of up to 303,000m3 of waste is to begin.
Mining at Konrad began in 1961 and ended in 1976, when further extraction became uneconomic. The mine has two shafts. The hoisting system in the southern shaft had been newly built and has been completely rehabilitated. In 2016, Siemag Tecberg was commissioned to examine options for converting the conveying system in the northern shaft from a guide rail system to a rope-guided system. In February 2017, a two-rope Koepe winding machine was commissioned and work began with the laying down of the ropes.
The completion of the north hoisting machine building at the beginning of 2020 was an important milestone on the way to commissioning the repository. The building is needed to house the technology of the northern hoisting system in Shaft 1.
In order to reduce the construction time for the new northern hoisting system, BGE, the body tasked with the final disposal of radioactive waste by the German state, opted for a system design with eight guide ropes for the new, main man riding system for northern conveying, which will consist of a two-rope Koepe hoisting machine. It will be operated in single-compartment mode with counterweight. For this purpose, the shaft must be rehabilitated, the guide frame in the surface area of the Konrad 1 shaft must be renewed, and the steel guide ropes must be anchored at the bottom of the shaft.
A strain energy linear ductile arrestor (or Selda – an overwind and safety arrestor) system is implemented as a safety device. As a conveyance, BGE envisages a combination of a skip with a container for the transport of debris (dead rock) as well as two decks for man riding or transport.
The installation of the hoisting machine took place under the management of Siemag Tecberg in March/April 2022. In later operation, the hoisting machine will realise a maximum payload of 15t when conveying material. The skip consists of two decks, whereby the lower deck of the skip must be converted for material conveying.
With man riding only, a total of 32 people can be transported on the two decks per hoisting cycle. The maximum conveying speed for material conveying is 16m/s, and 12m/s for man riding. The traction sheave of the new hoisting machine has a diameter of 5m and is connected to the machine shaft by means of HV screw connections. The machine shaft is supported on two plain bearings, one non-locating and one locating. The oil supply to the two bearings is placed in the basement of the hoisting machine building. In addition to the circulating oil lubrication, both bearings have a hydrostatic start-up aid, which serves to reduce the bearing wear. The two brake discs of the hoisting machine are bolted to the traction sheave on the front side.
The total of eight pairs of brake generators are mounted on four brake posts that enclose the brake discs from both sides. The braking force is generated by means of disc springs and transmitted to the brake discs. The brake shoes are released hydraulically.
A three-phase synchronous motor with 1,750kW of power as well as automation technology including the machine control complete the package of this hoisting system.
Until the new hoisting system on the north side of the shaft with its final depth of 1,232.5m is ready for operation, the hoisting system on the south side of the shaft will safeguard man riding and material transport at the Konrad shaft. The people working underground, all the machinery and equipment and the material are currently transported by this hoisting system.