Decanter Centrifuge Operation in Mud System

Decanter centrifuge is usually installed after the desilter in mud solids control system. The drilling mud from the desilter is pumped through the inlet to the feed chamber and slung from the feed ports into the pool. It is accelerated again with a high shearing effect due to the rotation of the bowl. The level of the pool is determined by adjustment of the weirs at the large end of the bowl (effluent discharge).
As the slurry flows through the pool in the channels between the conveyors flights, the particles settle according to Stocke's law, but at an accelerated rate due to the higher G forces. Sand particles settle almost instantly, then the finer particles settle. The particles that cannot be settled under the existing settings of the centrifuge will discharge out the overflow with the liquid phase (effluent).
The screw conveyor rotates in the same direction as the bowl, but at a slightly slower rate. This difference is determined by the gear box. Typical gear boxes are 80:1, 125:1, 40:1, and 52:1 gear box. 125:1 means that for every 125 revolutions of the bowl, the conveyor turns one less or 124. With this ratio, a centrifuge rotating at 1800 RPM has a conveying speed of 1800/125=14.4 RPM.
The settled solids from a cake on the side of the bowl and are conveyed along the outer edge of the pool towards the solids end (small end) of the rotating assembly and are discharged out the solids discharge ports at high velocity. As the solids travel across the beach, they lose their free liquid film due to centrifugal squeezing and drainage. They are discharged with only the absorbed moisture; provide the centrifuge is operated properly.

This discharge cake is very heavy, and sticky. It will not flow because of the lack of free liquid. It is important to realize this when installing a centrifuge. If possible, install over the place where the solids are to be discharged. If this is not possible and this slide so that it will self clean. If this is not possible, then some sort of mud wash or water wash will be needed to keep the solids from building up and packing off the centrifuge. Another option is a small amount of remix water added within the bowl housing directed at the solids discharge to softed the slurry. Remember to have the solids directed towards an mud agitator to keep the solids from simply dropping to the bottom of the mud tank.