The mud centrifuge which is also a settling device is designed to remove small, drilled particles while saving barite. It consists of a conveyor screw inside a cone-shaped bowl that is rotated at approximately 1600 to 1800 rpm. The conveyor screw rotates in the same direction as the bowl but 20-40 rpm slower.
Mud with dilution water is metered into the centrifuge through the hollow shaft in the conveyor screw. The mud is thrown to the wall of the bowl by the centrifugal force of rotation where it forms a pool. A circular row of ports at the large end of the bowl allows the liquid portion of the mud at the top surface of the pool to flow from the centrifuge. As the mud moves toward these overflow ports, solids settle toward the wall, where they are scraped by the conveyor screw toward the underflow ports at the small end of the bowl.
In this manner the mud is divided into two streams, the light overflow, which weighs approximately 9.5 lb./gal, and the heavy, concentrated underflow slurry, which weighs approximately 23 lb./gal.
Increased bowl speed increases the centrifugal force acting on the particles and increases their settling velocity. The bowl speed should be maintained at 1600 to 1800 rpm to effectively settle barite particles in the 3-4 micron range. Slower speeds allow more of the small barite particles to escape to the overflow and be discarded.