Siemens introduces Frozen Charge Shaker at Brazilian mine
Siemens has introduced a new technology – the Frozen Charge Shaker – that avoids interruption of production for removal of a solidified charge attached to a mill shell. The innovation is saving Kinross Gold time and money.
Siemens started the world’s first ore-grinding mill to be fitted with the company’s Frozen Charge Shaker function in December 2008, at Kinross Gold’s Paracatu gold mine in Brazil.
The new solution, which is integrated into Siemens’s Simine Mill GD gearless mill drive, removes charge that has become firmly attached (frozen) to the inside wall of the mill. This prevents the mill from being damaged as a result of charge falling down in an uncontrolled manner and also, simultaneously, reduces maintenance times.
Traditionally, the frozen charge problem has arisen when maintenance has had to be carried out on grinding mills, necessitating a shut down lasting several hours or days. In this time, the remaining mill charge can easily solidify, firmly attaching itself to the wall of the mill. This is called “frozen charge”.
When the mill is started again there is a danger that the frozen charge will not detach itself from the mill wall immediately but will initially be lifted up by the mill and then fall down from a great height. The resulting damage to the mill can be severe.
According to Siemens, gearless mill drives of the type Simine Mill GD come with a Frozen Charge Protection function that detects firmly attached charge in good time and switches off the mill. This prevents damage being done, but does not automatically eliminate the frozen charge.
Frequently, the material does not break up and remains stuck to the wall of the mill. This is why it used to be necessary to apply labour-intensive mechanical means to remove the firmly attached charge. This lengthens downtimes by hours or days and can lead to production outages costing several million US dollars.
In contrast, using the Frozen Charge Shaker function integrated in the Simine Mill GD system, Siemens says deposits can be loosened by causing the mill to move appropriately.
To do this, operating personnel initiate the Frozen Charge Shaker mode of the mill drive at the local control desk. The mill shell is then tilted at an angle so that any material that falls cannot damage the insides of the mill.
Specific alterations of the grinding tube’s acceleration and direction of rotation loosen the charge that is stuck on, thus causing it to be detached from the wall of the mill. The motor is the same one that is used for grinding.
Canadian miner Kinross Gold’s Paracatu open-cast gold mine is the largest single gold mine in the world in terms of ROM processing.
The mining site is near the historical gold-digger city of Paracatu, around 220 kilometres to the south-east of the capital, Brasilia. A 12-metre SAG (semi-autogenous grinding) tube mill, with a Simine Mill GD gearless drive system with an output of 20 megawatts, is used for crushing the ore.
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