Cross flow slurry filtration apparatus and method

A rotary filtration apparatus for the multistage filtering of an abrasive polishing slurry contained within a storage volume, comprising:

• an elongated inner filter assembly having a first end, a first longitudinal central axis of rotation, a second end, and a substantially cylindrical first filter surface with a first controlled porosity positioned therebetween to define a first interior volume, the inner filter assembly further having a first diameter;
• an elongated outer filter assembly having a first end, a second longitudinal central axis of rotation, a second end, and a substantially cylindrical second filter surface with a second controlled porosity positioned therebetween to define a second interior volume, the outer filter assembly having a second diameter larger than the first diameter;
• a substantially cylindrical elongated housing having an inlet opening, an outlet opening, a bypass opening, an intermediate inlet opening and an intermediate outlet opening and further having an internal cavity with a third diameter larger than the first or second diameters, the outer filter assembly being positioned within the internal cavity and accommodated within the cavity, and the inner filter assembly being positioned within the second interior volume of the outer filter assembly and accommodated within the cavity with the first longitudinal axis substantially parallel to the second longitudinal axis to define an intermediate annular volume between the inner and the outer filter assembly within the cavity, and an annular volume between the outer filter assembly and the housing, and having the first interior volume in fluid communication with the inlet opening through the first end of the outer filter assembly and the first end of the inner filter assembly, the bypass opening in fluid communication with the first interior volume through the second end of the outer filter assembly and the second end of the inner filter assembly, the intermediate inlet opening being in fluid communication with the intermediate annular volume through the first end of the outer filter assembly and the intermediate outlet opening being in fluid communication with the intermediate annular volume through the second end of the outer filter assembly, and the outlet opening being in fluid communication with the annular volume;
• a drive unit structured to rotate the inner filter assembly and the outer filter assembly capable of rotating the inner filter assembly and the outer filter assembly within the housing about an axis of rotation substantially parallel to the first and second axes of rotation, the inner filter assembly being rotated with a prescribed first angular velocity, and the outer filter assembly being rotated with a prescribed second angular velocity;
• a bypass line in fluid communication with the bypass opening and the storage volume to transport slurry therebetween;
• a intermediate line in fluid communication with the intermediate outlet opening and the intermediate inlet opening to transport slurry therebetween;
• a supply line in fluid communication with the storage volume and the inlet opening;
• and
• a pump positioned in the supply line to transport the slurry from the source of the polishing slurry to the inlet opening of the housing.

A method for filtering a polishing slurry, comprising:

• introducing an unfiltered slurry stream into a substantially cylindrical filter assembly having a central longitudinal axis of rotation that includes a filter material of controlled porosity;
• rotating the filter assembly about the axis of rotation to generate a shear layer adjacent to the filter material;
• passing a first fraction of the slurry through the filter material to obtain a filtered slurry;
• and
• bypassing a second fraction of the slurry from the filter assembly.