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Aug 20, 2021

Flotation mixing mechanism - wear vs performance study

Jukka Lakanen
Jukka Lakanen
Product Manager, Flotation Spares • Services/SVS Beneficiation & Dewatering
How does the wear of a mixing mechanism affect the flotation process? The flotation theory provides general reasoning on how wear might affect process performance. However, it does not much describe the phenomena. We have, therefore, prepared a computational fluid dynamics simulation with new and worn conditions of the mechanism in order to study and better understand the effects of wear.
CFD modelling
CFD modelling

When parts are new the slurry flow entering the cell is efficiently pumped through the impeller. The impeller disperses air and provokes turbulence into the slurry and causes particles and bubbles to collide and adhere. It also produces internal flow patterns in the cell to allow the bubbles to rise through the slurry. In the CFD studies, the evident wear on the rotor and stator was seen to weaken the ability to perform key functionalities needed for efficient flotation.

 

imagepti8.png

CFD results - particle time path lines (side view)

 

When a rotor is worn, power intake for the mechanism drops and the streams outwards from the impeller become smoother. This causes heavier particles to remain on the floor and pulp aeration also becomes less uniform. As the stator wears it loses some ability to resist the slurry flow, meaning less turbulence, and fewer opportunities for bubbles and particles to collide and attach. When both parts are worn, the power drop is enhanced.

With high wear rates the risk of short-circuiting, i.e. feed slurry leaving the cell without circulating through the impeller, increases. The CFD short-circuiting was seen at the bottom of the cell and under the impeller.

 

Summary

Rotor wear

Stator wear

Less power draw, pumping

Less mixing and turbulence

Less gas dispersion

Alters cell internal flows

Risk of short-circuiting new feed

Less bubble-particle collision

Flotation performance loss

Flotation performance loss

 

Conclusions

Wear of the mixing mechanism can have a negative effect on flotation performance as studied. Wearing is gradual and depends on pulp characteristics and rotation speed. To maintain performance, rotors and stators should be regularly inspected and kept in good condition.

Metso Outotec can provide support for evaluating the condition of the mechanism by supplying wear limit drawings and recommendations for Metso Outotec FloatForce and SkimForce mechanisms.

 

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