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The acknowledge of decanting centrifuge you must know

2012-09-08

The centrifuge is the last class of the whole mud cleaning system, it is used to separate the solid phases and liquid in drilling fluid or separate the liquid with different density in emulsion.
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The structure and working principle of centrifuge

Sedimentation centrifuge( screw type): It is use centrifugal sedimentation method to separate the composition of drilling fluid. The drilling fluid added into the drum forms the annular liquid layer under the force of centrifugal, the solid particles subside on the wall of drum. The clean liquid will be discharged from the overflow hole of drum or pipette, which is called chaotropic. When the separation finished, the sediments should be discharged manually or mechanically.
The centrifuge with high separation factor should be used when the density difference of solid and liquid is small, the size of solid phases is small or the viscosity of liquid is high. The centrifuge is to lengthen the residence time of drilling fluid in the rotating drum to guarantee the separated liquid clear.
The sedimentation centrifuge is widely used, especially used for the separation of drilling fluid with leakage of most fine particles or high filtration resistance because of the solid phases block the filtration medium. But the water content of the sediment will be high.
Sieve drum centrifuge (Drum): The inside drum with many holes rotates in a fixed cylindrical case, there is hydraulic seal at the two sides of the shell. The axis of the inside drum stretches out through the seal, after the drilling fluid and dilution water injected from the upper left of the shell, because of the rotating of the inside drum, the drilling fluid rotates in the space between the two drums. Under the centrifuge force, the barytes and other big solid phases will be thrown to the wall of the shell, and discharged from an adjustable chock mouth. Adjust the chock mouth and the speed of pump can adjust the flux of the bottom flow. The light mud will sink slowly, enter the inside drum and be discharged by hollow axle. This kind of centrifuge can deal with a large mount of drilling fluid, and recover 82%-96% of the barytes.

Based on the centrifugal force, rotating speed, separation points and admission capacity, the centrifuge can be classified as:

Barytes recovery centrifuge: The rotating speed is 1600-1800r/min. The centrifuge force is 500-700 times of gravity force. To the solid phases with low density, the separation point is 6-10um, and to the solid phases with high density, the separation point is 4-7um. The admission capacity of mud is 2.3-9 m3/h. This kind of centrifuge is used to clean the colloid and control the PV.
Large thruput centrifuge: The admission capacity of mud is 23-45 m3/h, the rotating speed is 1900-2000r/min. The centrifugal force is 800 times of gravity. The separation point is 5-7um. This kind of centrifuge is to deal with the solid phases larger than 5-7um.
High Speed Centrifuges: The rotating speed is 2500-3000r/min, the centrifugal force is 1200-2100 times of gravity. The separation point can reach 2-5um. The admission speed of mud is decided by the type of drilling fluid. This kind of centrifuge is used to separate the solid phases of 2-5 um.