The drum and the screw rotate at a high speed in the same direction at a certain differential speed. The material is continuously introduced into the inner cylinder of the conveying screw from the feeding pipe, and then enters the drum after being accelerated. Under the action of the centrifugal force field, the heavier solids are deposited on the wall of the drum A layer of sediment is formed. The conveying screw of the decanter centrifuge continuously pushes the deposited solid phase to the cone end of the drum, and discharges it out of the machine through the slag discharge port. The lighter liquid phase forms an inner liquid ring, which continuously overflows the drum from the overflow port at the large end of the drum, and is discharged out of the machine through the liquid discharge port. The decanter centrifuge can continuously feed, separate, wash and discharge materials at full speed. Due to the high-speed rotation and frictional resistance of the rotor, the sludge is accelerated inside the rotor and forms a cylindrical liquid ring layer. Under the action of centrifugal force, the solid particles with larger specific gravity settle to the inner wall of the drum to form a mud layer, and then the screw and the drum are used. The relative speed difference pushes the solid phase to the cone end of the drum. After pushing out the liquid surface, the sludge can be dehydrated and dried, and then pushed to the slag discharge port to be discharged. The supernatant is discharged from the large end of the drum to achieve solid-liquid separation.
The longer the residence time of the material in the drum, the greater the separation factor and the better the separation effect at the same speed. However, due to the limitation of materials, the diameter of the centrifuge drum cannot be increased indefinitely, because as the diameter increases, the maximum allowable speed will decrease with the decrease of the material's solidity, and the centrifugal force will decrease accordingly. Due to the centrifugal force, it is subjected to the downward sliding backflow force. An important parameter in the design of a decanter centrifuge. From the clarification effect, the cone angle is required to be as large as possible; from the slag conveying and dehydration effect, the cone angle is required to be as small as possible. Since slag conveying is a necessary condition for the normal operation of the centrifuge, the best design must first meet the slag conveying conditions. For difficult-to-separate materials such as activated sludge, the half-cone angle is generally within 6 degrees to reduce the return speed of the sediment. In order to ensure that the liquid phase has a sufficient settling distance, but the solid phase can only stay for the time it takes to pass through the cone, so a higher centrifugal force is required; the material entering the drum from here will cause the solid particles that have settled in this area. When the disturbance floats again, turbulence and additional eddy currents are also generated, which reduces the separation effect.