Potash, which is a crucial component of modern fertilizer, is found mixed with salt in nature. Mosaic’s three massive mines in Esterhazy, Saskatchewan use a “process brine” to separate the potash and the salt. Over time, the brine becomes saturated with clays called “slimes” which lower the brine’s efficiency. Mosaic uses a “thickener tank” to remove the slimes before recirculating the brine. The thickener tank takes the process brine and clarifies it by settling the “slimes” prior to it being recirculated back into the plant for the process.

Without a thickener tank, the Esterhazy mines can’t run — which means the old thickener rakes in the tank are mission-critical equipment.

Since 1975, the Esterhazy K1 mine site used a set of carefully maintained second-hand thickener arms. In 2021, the end of their service life arrived. Replacing them was a top priority for Mosaic and the project was a high-pressure job, with a critical schedule. Every hour the tank was offline during the replacement was another hour that the mill could not run. By the same token, any later problems with the thickener tank would also affect reliability of the K1 mill, so the margin for error during the upgrade was virtually nil. When it absolutely had to be done correctly and as quickly as possible, Mosaic teamed up with PCL.

The first step PCL’s Elliott Debolt, project manager, and Sheldon Dmytriw, superintendent, took to guide this rake replacement to success was to craft a very careful project plan. The two spent six weeks in a socially-distanced boardroom working with Mosaic to make a plan that was absolutely air-tight.

This started with deconstructing the initial estimate, identifying its operating assumptions, and then testing those assumptions to validate them. The planning team also found several opportunities to pre-assemble parts of the new rakes before the shutdown began, which lowered the project’s risk and shortened the mine’s idle time. Finally, the team identified all potential project risks and developed detailed plans to mitigate them.

All that careful work created a rock-solid plan that cut two days of downtime off the projected schedule and received approval from Mosaic’s senior leadership.

“Knowing that any time we could shave off the schedule would be more time milling for Mosaic, we basically did a full round of value engineering,” says Debolt. 

When the scheduled shutdown and replacement arrived in September of 2021, Debolt, Dmytriw and the team sprang into action. It wasn’t long before they hit their first bump in the road.

“The old rakes were, well, old,” says Debolt. “We ran into some as-found and design issues. There were lots of things we had to manage in our stride, however we were strategic during planning and had identified these ‘as-found conditions’ within our risk mitigation plans. The answers were already in place.

This is where the mitigation plans proved their worth.

“Our mitigation plans let us avoid lengthy conversations about how to solve problems during the shutdown,” says Debolt. “Instead, we could just focus on the work with all the solutions already discussed and agreed upon in advance.”

That involved coordinating dozens of skilled subcontractors to cut through the wall of the thickener tank, remove the old rakes, install new ones, replace the center column and trestle, and then repair the tank.

When the dust settled, over 20,000 hours of around-the-clock work was completed within the planned 19-day shutdown with no major errors or crises. The new thickening rakes are also set to meet Mosaic’s needs in Esterhazy for years to come.

“The project has been considered a resounding success by the client,” says Debolt. “I’m quite proud of my team for making this happen.”