Metso grinding mill minimises expenses
METSO’S grinding mill – customised precisely to the dimensions of the old equipment – proved to be the most economical solution for Yara Suomi’s phosphate mine in Siilinjärvi, Finland.
In the engineered- to- order ( ETO) project, a fully finished rod mill was installed in the mine’s concentration plant during a normal annual shutdown.
“A quick calculation already shows us that we received a new custom- built mill at half the cost of what a standard mill and the required new power transmission, electrification and foundations would have cost us,” Yara Suomi Siilinjärvi concentration plant manager Antti Savolainen said.
“We’ve noticed that most project expenses in old mill surroundings arise from the work that needs to be done in the immediate environment of the equipment in need of renewal.
“The old equipment’s replacement with a finished mill, carried out in 10 days during the annual shutdown, was also a much better option for us than a traditional on- site installation, which takes 24 days and would have prolonged the shutdown considerably. Given the strong demand for our concentrate and a daily production volume of around 2,800 tonnes, the customisation was well worth the investment,” Mr Savolainen said.
After Yara had ordered the tailor- made grinding mill in early 2017, Metso built an international team for the project.
The new 4x6 metre rod mill was designed in such a way that it could be installed precisely on top of the bearing housings of the old mill, installed in 1979.
The scantlings of the mill casing were thickened to 45 mm, and the ends were modernised to be replaceable.
Metso manufactured the grinding mill and the attendant plain bearings, and installed the mill lining.
The delivery also included the design and manufacture of a new installation cradle with a 350- metric- ton capacity, allowing the mill and its contents to be lifted when necessary.
Yara was able to utilise the entire old power transmission line, gearbox and foundations in the project.
The parts of the new grinding mill were shipped to a machine shop near Kuopio for assembly in 2018.
Weeks before the delivery, the new grinding mill was given its finishing touches – the bearing housings at the ends were attached, the interior was lined with protective plates, hundreds of mounting bolts were tightened, and the mill was painted in Metso’s beige color.
The mill, which weighed more than 150 tonnes, was transported to the mine on a 14- axle trailer in the week preceding the shutdown.
At Yara’s mine, the mill was lifted into place with a massive lattice boom crane, the crane hook of which was located at the end of a 60- metre boom.
The mill arrived at the site on a Tuesday and was installed within a week, with work resumed by the following Monday.
The rod mill now works 24/ 7, grinding the 25 mm ore feed into smaller pieces with 1250 kW of power and an hourly capacity of about 500 metric tonnes.
“Our target is for the new mill to grind phosphate ore at our mine with a 99.9 percent utilisation rate for the next 30 years,” Mr Savolainen said.