Drive design saves space

Adding a dozen bucket elevators equipped with shaft-mount planetary gear drives as part of a major expansion has saved space and reduced cleanup and maintenance at PotashCorp’s Rocanville mine in Saskatchewan.

The facility, in operation since 1970, mines and processes potassium chloride (KCl) in granular and standard forms for fertilizer.

In 2004, the mine underwent a major expansion that brought its capacity to three million metric tonnes per year. This made it possible to produce more of the product most preferred by much of the world marketplace.

Production of granular potash increased from 15-20% of the facility’s product mix to more than 70%. Included in the expansion was the addition of 12 new Rexnord Hi-load chain bucket elevators, which elevate the bulk dry product so it can be screened for sizing and recompacted or crushed if necessary.

To provide elevators for the expansion, PotashCorp selected the Rexnord Conveying Equipment Division, which draws upon power transmission products made by the firm’s various divisions to provide a broad range of material handling equipment and systems.

Elevator design customized to application

The elevators combine a sturdy design with ease of maintenance that has enabled them to be operated dependably and to continue to do so for many years. The elevators furnished to Rocanville are relatively slow-speed units (chain speed under 46 m or 150 ft per min.) with dual strands of Rexnord elevator chain and fixture-welded Rexnord Super Capacity steel buckets.

As the material is charged into an elevator, it flows directly into the upgoing strand of buckets through the use of ‘loading legs’ within the boot section, which help funnel the product into the bucket. Vent holes were added to the buckets to allow air to be released in applications where fine products are being handled.

The buckets are mounted in a unique overlapping style to enable continuous filling of the buckets. The buckets are designed to discharge the material so it cascades off the preceding bucket. This directs the material out of the elevator during discharge.

These elevators are driven by timed and matched head sprockets and guided by traction wheels on the foot shaft assembly, which is mounted to a gravity take-up arrangement that will internally adjust for slight chain elongation during the entire chain life without any manual maintenance.

The elevator casings are fixture-welded, dust-tight and braced in each corner with vertical corner angles that provide vertical support. They also include a 10- ga. casing enclosure for local dust removal in the intermediate sections and 6.4 mm-thick (0.25-in.) steel in the boot and lower head sections.

Frequent washdowns

The boot sections here are made of stainless steel to resist corrosion from frequent washdowns, but casing construction can be either stainless steel or carbon steel as required. It can also be manufactured with a custom surface preparation to customer specifications. A sealant is provided for all mating flange connections.

The 12 elevators vary in overall height from approximately 23.5 m to 40.8 m (77 ft to 134 ft), with centre-to-centre distances ranging from 23.6 m to 38.6 m (77 ft 7 in.