Page 168 - Shale Shakers Drilling Fluid Systems

SOLIDS CONTROL EQUIPMENT 151

microns). What is the D 50 cut point in a 50-cp vis- Again, cut point performance can be further
cosity fluid of the same density? projected by dividing by the projected specific
For constant settling velocity, if fluid density is gravity at various viscosities. Thus, in the above
unchanged and other parameters remain constant: example, for a 6-inch hydrocyclone, 20 centipoise
viscosity, and 1.4 (11.7 ppg) density fluid, the D 50
would be:

2 05
[(112 microns) x 1.1/1.4] = 99.3 microns
For p, = p 2
Hydrocyclone Operating Tips

• Other than cone and manifold plugging, im-
properly sized or operated centrifugal pumps
are by far the greatest source of problems
encountered with hydrocyclones. Centrifugal
pump and piping sizes are critical to efficient
hydrocyclone operation.
• Hydrocyclones should always have a pressure
gauge installed on the inlet manifold to quickly
determine if proper feed head is supplied by
Thus, if fluid specific gravity remains 1.1 and viscos- the centrifugal pump.
ity is 50 centipoise, the D 50 is raised to 85 microns.
Similarly, for a 4-inch hydrocyclone: • Hydrocyclones are usually mounted in the
vertical position but may be mounted hori-
Fluid viscosity (cp) D 5y microns (sp. gr. = 2.6) zontally. Cone orientation is irrelevant be-
cause the separating force is supplied by the
1.0 12.0 centrifugal pump.
10.0 37.9
• Feed slurry must be distributed to a number of
20.0 53.7
hydrocyclones operating in parallel. A "radial
30.0 65.8
40.0 75.8 manifold" provides each cyclone with the same
50.0 84.8 slurry (in terms of feed solids concentration
and particle size distribution) and at the same
pressure. An "in-line" manifold guarantees the
Cut point performance can be further projected
by dividing oy the projected specific gravity at higher mass (larger diameter) particles pass the
first cyclones and, instead, enter the last cones.
various viscosities. Thus, in the above example, for
Because these particles have a higher energy,
20 centipoise viscosity and 1.4 (11.7 ppg) density
fluid, the D 50 would be: they resist entering the first cones. Thus, the
last cones in an in-line manifold receive a
05
2
[(53.7 micron) x 1.1/1.4] = 47.5 microns higher concentration of coarse feed particles.
Cone performance in an in-line manifold will
not be identical since feed concentrations
The D 50 cut point for 6-inch and 8-inch hydro- and particle size distributions differ for vari-
cyclones (common desilter and desander sizes) are ous cones. Further, if the last cyclone(s) in an
usually given as 25 and 60 microns, respectively. in-line manifold is taken off-line, the end of the
The variation of D 50 cut point with viscosity for manifold has a tendency to plug.
a 6-inch desilter hydrocyclone (specific gravity =
1.0) is as follows: • To minimize loss of head along the feed line
and backpressure on the overflow (top) dis-
Fluid viscosity (cp) D 50, microns (sp. gr. = 2.6) charge line, keep all lines as short and straight
as possible with a minimum of pipe fittings,
1.0 25.0
turns, and elevation changes. Pipe diameters
10.0 79.0 should be 6 or 8 inches.
20.0 112
30.0 137 • Operate cones in spray discharge with a cen-
40.0 158 tral air suction, and check cones regularly to
50.0 176 ensure the apex discharge is not plugged.