What is a feedwell?
A thickener feedwell is where the feed slurry is delivered by feedpipes, channels or launders. It is predominantly located centrally and can be as simple as an open cylinder.
It is usually expected to:
- Contain and dissipate the momentum of the incoming feed while ensuring a symmetrical solids discharge to the settling zone below, and
- Provide the required turbulence for effective mixing of the flocculant amongst the feed particles, such that aggregates grow to sizes that favour rapid settling, fine particles are well captured, and irreversible aggregate breakage is not extensive.
The biggest design problem is to dissipate and evenly distribute the residual momentum of the incoming feed stream. The velocity of the fluid in the feed pipe generally needs to be 1 to 2 m s-1 to keep feed solids in suspension. There are three commonly used ways of converting this velocity to random turbulence and eventual decay: deflecting baffles, devices that break-up the stream into smaller ones and the impingement of opposing jets (as seen in Bayer feedwells). All three have been tried in a variety of designs, although few are particularly effective.
A representation of ideal feedwell performance is given below (blue is for feed particles, red is for the largest aggregates formed).
