Efficient flotation: Designing the optimal bubble

The flotation team knew they could improve the energy efficiency of flotation by rethinking the rotor/stator technology. So they teamed up with aerospace researchers and changed the hydrodynamics of the flotation system.

"Smaller bubbles have better attachment properties than large ones. But if you increase aeration rate to improve throughput, the flotation cells produce larger, not smaller bubbles, so it's really not a straightforward proposition," explains Product Manager of Flotation at FLSmidth, Asa Weber.

Flotation is about creating the proper energy dissipation rate in the cells, to obtain optimal contact between the bubbles and the particles and extracting the minerals.

"We wanted to design a machine that enabled us to increase the air volume and reduce the bubble size at the same time and simultaneously optimise energy dissipation rate. So for the initial technology developmental phase we decided to team up with a range of experts in air dispersion; including aerospace researchers, surface chemistry researchers and the Center for Advanced Separation Technologies at Virginia Tech. We worked with a 3-phase model replicating real world conditions," says Weber.

The combination of mining industry academics and experts from the aerospace industry allowed the team to come up with an innovative design concept for the rotor/stator.

"They admitted it was difficult. They know about high-performance aircrafts and submarines and we wanted them to deal with a three-phased flow problem," Weber laughs.

New rotor/stator low-energy technology

The target was to create a new ultralow-energy flotation system and the team came up with the nextSTEP™ advanced flotation mechanism, featuring a new rotor/stator low-energy technology.

The function of the rotor/stator is to make bubbles, suspend particles and create an environment for bubbles and particles to make contact. "The key is to do it with the least amount of power possible. So we elongated the vane of the rotor and cut slots in the stator to optimise the geometry of the rotor/stator assembly," Weber explains.

We wanted to design a machine that enabled us to increase the air volume and reduce the bubble size at the same time and simultaneously optimise energy dissipation rate
— Asa Weber, Product Manager of flotation, FLSmidth

The new rotor is designed to produce ideal flow streams. It also produces an energy dissipation rate that enhances the bubble-particle attachment. The patented rotor/stator makes energy dissipation more uniform, which results in a higher probability of bubble to particle contact during the flotation process, dramatically improving attachment rates. The jet exiting the rotor is distributed across a larger surface area than in traditional machines and this causes an even flow distribution that increases the wear life of the mechanism, as well as reducing downtime for repairs. On top of the even wear patterns, the rotor can also be run in a reverse direction to further increase the life cycle of the mechanism.

"The nextSTEP rotor/stator provides a step change in flotation, metallurgical performance and energy efficiency," Weber states: "It has the lowest operating power of any forced-air flotation mechanism on the market."

Up to 40% less energy and compatible with all cells from other suppliers

  • 15-40% less energy consumption, while maintaining or improving recovery.
  • Engineered to fit a variety of machine sizes, ranging from the smallest 5 m3 cell up to FLSmidth’s 660 m3 SuperCell™ machine.
  • Interchangeable with FLSmidth's Dorr-Oliver® forced-air flotation mechanisms.
  • Installation of the nextSTEP mechanism can be carried out during scheduled maintenance downtime because the components of the system are common items that must be replaced periodically within ongoing flotation operations.
  • The design is applicable across all mineral applications and can also be retrofitted into cells from other suppliers. An energy saving of 18% was obtained in a copper plant by exchanging the existing rotor/stator in a cell from another supplier with the nextSTEP mechanism.
  • Analysis of the wear characteristics after nine months in operation indicates that the wear life of the nextSTEP will exceed the industry benchmark of two years.

Contact:

Steve Ware, Director for flotation and dewatering: Steve.Ware@FLSmidth.com

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