A hydrocyclone (often referred to by the shortened form cyclone) is a device to classify, separate or sort particles in a liquid suspension based on the ratio of their centripetal force to fluid resistance. This ratio is high for dense (where separation by density is required) and coarse (where separation by size is required) particles, and low for light and fine particles. Hydrocyclones also find application in the separation of liquids of different densities.

Since most hydrocyclones are designed to operate at a constant 75 feet
of head at the input manifold, flow rate through any cone is constant
at constant inlet pressure for a given fluid viscosity.

The smaller desilter hydrocyclones are rated from 40 to 100 gpm of
liquid removal, depending on the cone design. The normal 4-inch cones
will remove 4 gpm of solids, or 5.7 barrels per hour of solids, per cone.
Therefore, a 16-cone desilter manifold will accommodate removal of
510 cubic feet of solids per hour. For a 17-inch hole, this equates to
penetration rates averaging 297 feet per hour. Clearly, if design and
operational characteristics are adequately maintained, more than ample
solids separation can be effected.

For deepwater drilling applications, higher flow rates are encountered
when boosting the riser. Additional cones may be needed to handle the
additional flow rates to ensure that the cone manifolds process all of
the mud.

The accelerated gravitational forces generated in hydrocyclones are
inversely proportional to the radius of the hydrocyclone cylinder. Thus,
the larger the diameter of the cone, the coarser the separation. In general,
the larger the hydrocyclone, the coarser its cut point and greater its
throughput. The smaller the cone, the smaller the size of particles the
cone will separate. In other words, the median particle size removed
decreases with cone diameter. Median particle size also increases with
increasing fluid viscosity and density, but decreases as particle-specific
gravity increases. Oilfield hydrocyclones range between 4 and 12 inches,
based on the inner diameter of the intake cylinder. A small hydrocyclone
diameter is used for ultra-fine separations.

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