# Unregulated Mechanical Factors of Decanter Centrifuge

**Unregulated Mechanical Factors of Decanter Centrifuge**

A. Drum diameter and effective length

The larger the diameter of the drum and the longer the effective length, the larger the effective settlement area will become, the larger the processing capacity. And the longer the residence time of the material in the drum. At the same speed, the larger the separation factor, the better the separation effect. However, due to the limitation of the material, the diameter of the drum of the decanter centrifuge cannot be increased indefinitely, because the maximum allowable speed will decrease as the solidity of the material decreases, and the centrifugal force will correspondingly decrease. Generally, the diameter of the drum is between 200 and 1000 mm, and the aspect ratio is between 3 and 4. The current development of decanter centrifuges tends to have a large aspect ratio with a high rotation speed. This Decanter centrifuge is more suitable for the treatment of low-concentration sludge, and the degree of mud biscuit is better.

In addition, in the case of the same processing capacity, the centrifuge with a large drum diameter can run at a lower differential speed, because the spiral slag conveying capacity of the large drum diameter is larger. To achieve the same slag conveying capacity, a centrifuge with a small drum diameter must be achieved by increasing the differential speed.

B. Drum's half cone-angle

When the sediment settled inside the drum is pushed to the discharge port along the end of the drum cone, it is subjected to the downward flow of the backflow force due to the centrifugal force. The half cone angle of the drum is an important parameter in the decanter centrifuge design. In terms of clarification effect, the cone angle is required to be as large as possible; and in terms of slag conveying and dehydration effects, the cone angle is required to be as small as possible. Since the slag transfer is a necessary condition for the normal operation of the centrifuge, the optimal design must first meet the slag transfer conditions. For materials that are difficult to separate, such as activated sludge, the half cone angle is generally within 6 degrees, in order to reduce the reflux speed of sediment. For ordinary general materials, the half cone angle is within 10 degrees to ensure the smooth transportation of sediment.

C. Pitch

The pitch, which is the distance between two adjacent spiral blades, is an important structural parameter that directly affects the success or failure of slag transport. When the spiral diameter is constant, the larger the pitch and the larger the spiral rise angle, the greater the chance that the material will be blocked between the spiral blades. At the same time, a large pitch will reduce the number of turns of the spiral blades, resulting in uneven material distribution at the cone end of the drum and causing increased machine vibration. Therefore, for difficult-to-separate materials such as activated sludge, it is difficult to convey slag, and the pitch should be smaller. Generally, the diameter is 1/5 to 1/6 of the drum diameter to facilitate transportation. For easy-to-separate materials, the pitch should be larger, generally 1/2 to 1/5 of the diameter of the drum, in order to improve the sediment transportation capacity.