Yara’s phosphate mine minimizes project expenses and installation time with Metso’s custom-built grinding mill

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. 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,” says Antti Savolainen, Manager of Yara Suomi’s Siilinjärvi concentration plant.

”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 tons, the customization was well worth the investment,” adds Savolainen.

The 18-month project was carried out by an international team

After Yara had ordered the tailor-made grinding mill in early 2017, Metso built an international team for the project. The key operators in mill manufacturing were the ETO group in York and Metso’s local project manager in Finland.

The new 4×6-meter 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 modernized 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 utilize the entire old power transmission line, gearbox and foundations in the project. The original gearbox was given a thorough overhaul during the shutdown.

Assembly of grinding mill close to the mine

The parts of the new grinding mill were shipped to a machine shop near Kuopio for assembly in March of this year. 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 weighs more than 150 tons, 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-meter boom.

Mill arrival on Tuesday, back to work on Monday

At the beginning of Yara’s annual shutdown, the roof of the concentration plant was opened, and the old mill manufactured by Wärtsilä was lifted out. On Tuesday, the new, more than 150-metri- ton rod mill was successfully set into place. The most time-consuming part was the final ten centimeters of the lowering, at which point the bearing housings were settled in their installation collars with millimetric precision.

Lauri Ylönen, the Maintenance manager for the mining sector in Finland, and his team worked in cooperation with the project manager Rainer Harmainen as well as with Yara’s Concentration plant manager Antti Savolainen and Maintenance manager Anssi Pietarinen to ensure that all work phases were carried out correctly and safely. The installation was also supervised by Rob Fielder from Metso’s US organization.

Following a pressure test carried out with water, the new mill was fitted with 800 grinding rods, after which the grinding of phosphate ore was ready to begin on schedule the following Monday. The rod mill now works 24/7, grinding the 25 mm ore feed into smaller pieces with 1,250 kW of power and an hourly capacity of approximately 500 metric tons.

“A cost-effective mine needs reliable equipment suppliers”

Antti Savolainen, Manager of the concentration plant, emphasizes the significance of the support that an equipment supplier can provide to the operations of a cost-effective mine:

“We want to rely on our partners and the know-how they provide. Metso has a good track record at Yara’s Siilinjärvi mine: it supplied the optimization of the linings of primary gyratory crushers and deliveries for the installation of an MP800 cone crusher. Now it looks like this custom-built mill solution that Metso proposed for us was also the right solution.”

“Our target is for the new mill to grind phosphate ore at our mine with a 99.9 percent utilization rate for the next 30 years,” says Savolainen.