As IM goes to press on its November issue, which includes a feature on Drives and Controls, one of the leaders in this space, ABB, reflects on the spate of new copper miners to have opened up in South America, Russia and Kazakhstan, and the drive solutions powering them forward.
This online editorial feature also comes as ABB’s solution for the Cobre Panama open-pit copper mine moves into continuous operation.
Gearless mill drives (GMDs) are the grinding solution of choice in challenging environments. By eliminating bolt-on mechanical components such as ring-gears, pinions, couplings and gearboxes, GMDs offer ore producers unrivalled availability, efficiency and durability, while reducing operating expenditure, according to GMD provider ABB.
“Both ring-geared mill drives and GMDs can be employed to drive autogenous, semi-autogenous (SAG) and/or ball mills,” says Marcelo Perrucci, Global Product Line Manager, Grinding, at ABB.
“The applications may be the same, but the challenge now is to develop bigger drivetrains with the power to drive these larger grinding mills – and this is exactly where GMDs come into their own.”
Unlike more traditional ring-geared mill drives – where a ring-shaped gear encircles the mill and drives it through one or two pinions followed by conventional motors – GMDs work by mounting rotor poles directly to the mill body and surrounding it with the stator ring, meaning the mill itself is incorporated into the motor.
The necessary torque to turn the mill is transmitted between the GMD motor and the mill via the magnetic field in the tiny air gap between the stator and rotor. Because this type of motor system requires no gearing or direct contact transmission, GMDs boost efficiency by reducing frictional losses, while fewer mechanical critical components means less maintenance downtime is required due to wear and tear, according to ABB.
“GMDs offer the highest power and availability compared to other driving methods,” confirms Perrucci. “Efficiency gains are possible by eliminating mechanical components that may fail and add unexpected and costly bottlenecks in the production process.”
ABB GMDs use a high efficiency cycloconverter to drive the motor. The same efficiency applies to other system components like transformers and the motor control centres incorporated into ABB’s E-house solution called Control Block; together, these advancements can boost energy optimisation in grinding mills by as much as 3%, according to the company.
“That equates to a significant amount of money saved, especially when you consider that some modern mines may have as many as six 15–25 MW GMDs running in parallel,” explains Perrucci.
Advancements in big data, and digital technologies such as the industrial internet of things, the cloud, data analytics, artificial intelligence and advanced modelling algorithms now offer mining companies unprecedented visualisation and transparency along the entire mine production chain, enabling them to carry out predictive rather than reactive maintenance operations from remote locations.
Using the ABB Ability™ cloud platform, GMD operators can access key system parameters, gathering and collating real-time data from sensors in the system, everything from insulation monitoring to status of the air gap to the temperature of rotor poles and stator windings.
Every hour of unplanned shutdown in a mine can cost the operator hundreds of thousands of dollars. Predicting when key parameters will reach critical levels and halt production is, therefore, crucial.
Using data sets collected from the GMD that are processed by specialised algorithms in the ABB Ability Cloud platform, together with ABB engineers, critical situations can be predicted and then timely notify customers in advance, avoiding costly downtimes.
Perrucci uses a real-world example to illustrate the point: “The system alerted us to the fact that there was an anomaly in the air gap between the rotor and the stator,” he recalls. “The ABB Ability predictive maintenance system sent an automatically generated SMS and email to the customer and to ABB’s lifecycle manager advising them to check it. They stopped the machine and found a small nut in the air gap that could have scratched the insulation and maybe even caused something more serious. An investigation followed as to identify why the nut was there in the first place and the most plausible cause was that somebody accidentally dropped it while inspecting the machine.
“We have reports from customers that almost 100 hours of downtime have been avoided by using this proactive approach to servicing,” he said.
Perrucci added: “All this is only possible if the machine has the right instrumentation in place.
“Much like a passenger airplane, GMDs are equipped with dozens of sensors to protect it and help the operators to run it smoothly. ABB makes no compromise in its availability-centred design. Our focus is not to eliminate critical protection components of the system to cut costs. We want to give operators peace of mind and allow them to embark on the 4th Industrial Revolution. This is only possible if we have the right instrumentation in place as well as a robust condition monitoring system. To date, ABB has the capability to remotely support over 100 mills in operation, while over 30 of them are already benefiting from our ABB Ability predictive maintenance platform.”
Improving insulation and preventing moisture ingress
Water and moisture ingress can potentially be a significant issue in ring motors, especially at sites with high levels of precipitation and humidity. In 2005, ABB modified its insulation system and, more than 100 machine years and 6 million operating hours later, no major problems have been reported.
“Our heat exchangers – located in the cooling box structure – are solely installed on the bottom of the motor, for example, meaning there is no risk of water ingress elsewhere, whereas in non-ABB GMD designs the cooling boxes are placed around the stator, increasing the risk of water leakage,” explains Perrucci.
“We also use leak detection instrumentation in the cooling boxes, humidity and air temperature sensors, differential pressure transmitters and flow meters to detect any leak due to any changes in these parameters.
“Our single-bar winding design concept allows for full continuous vacuum pressure impregnated insulation. We can also employ online partial discharge monitoring, especially when the mine is situated in high altitude areas, such as in Chile and Peru.”
Case studies: Aktogay and Bozshakol
ABB has partnered with Kaz Minerals to supply GMDs for the company’s Aktogay and Bozshakol copper mines in Kazakhstan, both of which are expected to process 25 Mt/y of ore.
ABB was awarded a multi-million contract to provide a 28 MW GMD for a 40 ft (12.2 m) SAG mill and two 22 MW drives for a pair of 28 ft (8.5 m) ball mills at Aktogay, and three identical systems at Bozshakol. Each includes phase and excitation transformers, a ring motor with a local mill control panel, and a containerised electrical house (E-house) including cycloconverter and advanced specific grinding control software.
“We are currently working on the expansion of Aktogay, which aims to double its capacity,” explains Perrucci. “ABB will install an additional 40 ft, 28 MW SAG mill and two 28 ft, 22 MW ball mills to the project in order to meet the challenge of higher-capacity production coupled with low ore grades.
“It obviously costs operators less in terms of capital expenditure to expand existing operations rather than build a new mine, and we have added more digital streaming capabilities to these new GMDs.
Since the first GMD was delivered in 1969, ABB has sold more than 130 units in 23 countries and currently has over 50% market share, it says.
“We are investing a lot in the ABB Ability platform and also improving our existing GMDs to make them even better in terms of predictive modelling,” says Perrucci. “ABB is also working on digital twin technology, using augmented and virtual reality for training and maintenance.
“This will allow us to build up a virtual picture of the GMD system and environment so that maintenance can be carried out in the mixed reality platform before it is applied to the actual machine.”