Centrifugal separator with a control unit for speed control

A method for separating solid particles from a liquid mixture in a centrifugal separator, the method comprising:

• providing a centrifugal separator comprising:
• a rotor body which having a vertical axis of rotation, the rotor body having a separation chamber with an inlet for the liquid mixture, the inlet being positioned above the separation chamber, the separation chamber comprising a stack of truncated conical separation discs disposed therein, the separation discs having at least one flow channel formed therein, the rotor body having a weight suitable for cyclic acceleration between a separation phase and a particle discharge phase,
• a first liquid outlet in communication with the at least one flow channel,
• a second liquid outlet in communication with the at least one flow channel and the first liquid outlet and the second liquid outlet being positioned above the separation chamber,
• a sludge outlet separate from the first liquid outlet and the second liquid outlet and being positioned on a bottom side of the centrifugal separator,
• a screw conveyor adapted to rotate in the rotor body around the vertical axis of rotation, at a conveyor speed differing from the rotational speed of the rotor body,
• a drive arrangement in communication with the rotor body and the screw conveyor, and
• a control unit in communication with the drive arrangement;
• the control unit receiving incoming signals from at least one sensor arrangement, processing the incoming signals and generating control signals and transmitting the control signals to the drive arrangement so that the control unit controls the drive arrangement to control the speed of both the rotor body and the conveyor during both the separation phase and the particle discharge phase, the control unit being adapted;
• rotating, with the drive arrangement, the rotor body and the screw conveyor around the vertical axis at their respective speeds;
• discharging a first separated liquid from the liquid mixture via the first liquid outlet;
• discharging a second separated liquid from the liquid mixture via the a second liquid outlet, the second separated liquid having a density greater than that of the first separated liquid;
• rotating the screw conveyor in the rotor body around the vertical axis of rotation, at a conveyor speed differing from the rotational speed of the rotor body, for transporting the separated solid particles in the separation chamber towards and out of the sludge outlet;
• controlling the drive arrangement, via the control unit, to rotate the rotor body at a first speed during the separation phase and at a second speed, which is lower than the first speed, during the particle discharge phase;
• increasing sludge discharge, via the control unit, by decreasing rotor speed so that the sludge discharge during the particle discharge phase is greater than the sludge discharge during the separation phase;
• controlling the drive arrangement, via the control unit, thereby cycling the centrifugal separator through operations in the separation phase and the particle discharge phase;
• cyclically accelerating the rotor body between the separation phase and the particle discharge phase;
• controlling, with the control unit, the drive arrangement to rotate the rotor body at the first speed during the separation phase for a first predetermined time based on a magnitude of a sludge layer extending radially inward from an inner wall of the rotor body, as measured by the at least one sensor arrangement, after the first predetermined time in the separation phase the control unit automatically initiating the particle discharge phase for a second predetermined time based upon a quantity of sludge discharged from the rotor body, as measured by the at least one sensor arrangement and during which the control unit controls the drive arrangement to control the rotor body at the second speed and to control conveyor speed, thereby discharging the separated particles via the sludge outlet, separate from the separated liquid;
• and
• controlling, via the control unit, the drive arrangement to accelerate the rotor body to the first speed, after the second predetermined time in the particle discharge phase.