Basics of Hydrocyclones

(Figure 14 shows a cut-away drawing of a hydrocyclone.) It has no moving parts, only the mud moves. Mud enters the upper, large cylindrical section tangentially to cause spiralling fluid flow. As fluid spirals toward the smaller end, this creates centrifugal force to make particles move toward the outer wall and then downward toward the opening at the bottom of the cone. Mud returns to the system out the top center through the vortex finder opening.

Figure 14 Hydrocyclone

Feed Inlet

Feed

Chamber

Figure 14 Hydrocyclone

Feed Inlet

Feed

Chamber

Hydrocyclone Calculations

Vortex Finder

| Liquid Discharge Opening (Overflow)

Vortex Finder

0|Solids Discharge Opening (Underflow)

The so-called cut-point of hydrocyclones is the size of particle (sand in water) that has 50:50 chance of either exiting at the bottom of the cone for discard or returning to the mud through the vortex finder. A published cut-point is not directly applicable to muds because of differences in fluid viscosities and particle size, shape, and composition. (Figure 15 shows cut point for a mud based on the amount of feed head. Cut point is a function of cone size, mud viscosity, feed pressure, or centrifugal forces developed due to velocity.) Without sufficient feed pressure from the pump, the hydrocyclones will not work as well as they should.

Figure 15

Cut Point of Hydrocyclone as a Function of Feed Head

Figure 15

Cut Point of Hydrocyclone as a Function of Feed Head

Hydrocyclon

To operate a hydrocyclone in balanced condition, the flow out the bottom discharge opening should be a slow spray of liquid and solids. An opening which is too large will discharge too much liquid; an opening which is too small will retain too many solids. When a mud is loaded with drill solids, the cone may eject the solids in a rope. This means the cut point is not as small as it would be if it were operating in spray discharge. Roping is not the normal operating mode, because solids are not being removed at top efficiency. If roping is a continual problem, a larger number of desilter cones or finer shaker screens should be used to lighten the load.

Hydrocyclones should not be operated for very long on a weighted mud because barite will be discarded due to its higher density. For example, a barite particle of 50 microns diameter will be processed the same as a drill solid particle of 74-microns diameter.

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