Method and apparatus for continuously separating a more dense fraction from a less dense fraction of a pulp material

An apparatus for separating more dense particles from less dense particles contained in a slurry, comprising:

• a) a rotary chamber with an inner wall separating outer and inner portions of the chamber, the inner wall including a screen;
• b) liquid supply means;
• c) a drive arrangement for rotating the chamber relative to the liquid supply means;
• d) a feed arrangement for supplying slurry to the inner portion of the chamber;
• e) a radial outlet in the outer portion of the chamber for the more dense particles which pass through the screen and the liquid in which they are suspended;
• f) a further outlet defined by the chamber inwardly of the screen for the less dense particles and liquid in which they are suspended;
• g) an inlet to the outer portion of the chamber for receiving a continuous supply of elutriation liquid from the liquid supply means;
• h) a surface in said outer portion of the chamber to direct the elutriation liquid to effect elutriation at said screen;
• and
• i) an accelerating structure for radially accelerating the elutriation liquid from the liquid supply means to the said inlet.

A centrifugal separator apparatus for separating more dense particles from less dense particles in a slurry, comprising:

• a rotor assembly;
• and
• a stationary assembly supporting said rotor assembly, said rotor assembly comprising:
• a bowl open upwardly to receive a supply of slurry;
• a hutch chamber surrounding said bowl and having a ring of peripheral discharge outlets;
• a vertical rotary drive shaft coupled to said bowl for rotating said bowl with said hutch chamber about a vertical axis;
• said bowl comprising a lower impermeable portion coupled to said drive shaft, an upper impermeable portion connected to said lower portion, and a frusto-conical screen, said screen forming an inner wall of said hutch chamber and being mounted on said upper portion;
• a feed plate mounted to a central region of said lower portion of the bowl to receive said supply of slurry and distribute said slurry centrifugally in the bowl;
• an annular liquid inlet for supplying elutriation liquid continuously to the interior of said hutch chamber;
• and a plurality of liquid inlet conduits for supplying pulses of liquid to the interior of said hutch chamber;
• said bowl further comprising a dam at an edge of said screen remote from said upper portion, and said lower portion defining a liquid outlet below said feed plate;
• and said stationary assembly comprising:
• a device for applying rotary drive to said rotary drive shaft;
• a support for supporting said rotary assembly;
• and
• an annular liquid chamber coaxial with said rotary drive shaft and comprising a supply for continuously supplying elutriation liquid to said annular liquid inlet, said annular liquid chamber further comprising a plurality of supply output ports disposed for intermittent communication with said plurality of liquid inlet conduits during rotation of said rotor assembly.

A method of separating particles suspended in a slurry according to particle density comprising the steps of:

• a) supplying slurry to an inner portion of a rotating chamber to form a layer of slurry on the inner surface of the screen separating the inner portion of the chamber from an outer portion of the chamber;
• b) supplying a continuous flow of elutriation liquid to the outer portion of the chamber;
• and
• c) radially accelerating the continuous flow of elutriation liquid at its entrance to the outer portion of the chamber.

A method of separating particles suspended in slurry according to particle density comprising the steps of:

• a) supplying slurry to an inner portion of a rotating chamber to form a layer of slurry on the inner surface of a screen separating the inner portion of the chamber from an outer portion of the chamber,
• b) supplying liquid in pulses to the outer portion of the chamber to pulse liquid from the outer portion of the chamber inwardly through the screen and layer of slurry thereon whilst allowing denser particles which pass outwardly through the screen to enter the outer portion of the chamber and allowing the less dense particles and liquid in which they are suspended to escape over the screen from the inner portion of the chamber;
• c) simultaneously supplying a continuous flow of elutriation liquid to the outer portion of the chamber separately from the liquid in pulses;
• and
• d) directing the elutriation liquid through the screen from the outer portion of the chamber to the inner portion of the chamber to effect elutriation at the screen.