Hydrocyclones

Hydrocyclones (also referred to as cyclones or cones) are simple mechanical devices, without moving parts, designed to speed up the settling process. Feed energy is transformed into centrifugal force inside the cyclone to accelerate particle settling in accordance with Stoke's Law. In essence, a cyclone is a miniature settling pit which allows very rapid settling of solids under controlled conditions.

Hydrocyclones are important in solids control systems because of their ability to efficiently remove particles smaller than the finest mesh screens. They are also uncomplicated devices, which make them easy to use and maintain.

A hydrocyclone (see Figure 3-20)

LIQUID DISCHARGE

FEED NOZZLE

DRILLING MUD

LIQUID DISCHARGE

FEED NOZZLE

DRILLING MUD

Vortex Nozzle

CLEANED DRILLING MUD (OVERFLOW)

VORTEX FINDER

SAND AND SILT, DRIVEN TOWARD WALL AND DOWNWARD IN ACCELERATING SPIRAL

SAND AND SILT (UNDERFLOW)

CLEANED DRILLING MUD (OVERFLOW)

VORTEX FINDER

SAND AND SILT, DRIVEN TOWARD WALL AND DOWNWARD IN ACCELERATING SPIRAL

SAND AND SILT (UNDERFLOW)

Figure 3-20 Hydrocyclone consists of a cylindrical/conical shell with a small opening at the bottom for underflow discharge, a larger opening at the top for liquid discharge through an internal "vortex finder", and a feed nozzle on the side of the body near the cylindrical (top) end of the cone.

Drilling mud enters the cyclone using energy created by a centrifugal feed pump. The velocity of the mud causes the particles to rotate rapidly within the main chamber of the cyclone. Heavy, coarse solids and the liquid film around them tend to spiral outward and downward for discharge through the solids outlet. Light, fine solids and the liquid phase of the mud tend to spiral inward and upward for discharge through the liquid outlet.

Design features of cyclone units vary widely from supplier to supplier, and no two manufacturers' cyclones have identical operating efficiency, capacity or maintenance characteristics.

In the past, cyclones were commonly made of cast iron with replaceable liners and other wear parts made of rubber or polyurethane to resist abrasion. Newer designs are made entirely of polyurethane, and are less expensive, last longer, and weigh less.

Most well designed oilfield cyclones operate most efficiently when 75 feet of inlet head (±5 ft) is applied to the cone inlet.

Centrifugal pumps must be properly sized for cones to operate efficiently. Centrifugal pumps are constant energy (head) devices and not constant pressure devices. Feed head is constant regardless of mud weight; pressure varies with mud weight.

Although centrifugal pump theory and sizing exercises are beyond the scope of this text, if you are not able to properly size your centrifugal pump to create 75 feet of inlet head to your set of cyclones, it is highly recommended that you contact the Technical Services Staff at Brandt / EPI™ for assistance. Remember, more errors in hydrocyclone applications are made with centrifugal pumps, rather than with the cyclones themselves.

The size of oilfield cyclones commonly varies from 4" to 12". This measurement refers to the inside diameter of the largest, cylindrical section of the cyclone. In general — but not always — the larger the cone, the coarser its cut point and the greater its throughput. Typical cyclone throughput capacities are listed in Figure 3-21.

Manifolding multiple cyclones in parallel can provide sufficient capacity to handle the required circulating volume plus some reserve as necessary. Manifolding may orient the cyclones in a vertical

CONE SIZE (I.D.)

4"

5"

B"

8"

10"

12"

CAPACITY (GPM)

50-75

70-80

100-150

150-250

400-500

400-500

FEED PRESSURE (PSI)

30-40

30-40

30-40

25-35

20-30

20-30

Figure 3-21 Hydrocyclone Capacities

Figure 3-21 Hydrocyclone Capacities position or nearly horizontal — the choice is one of convenience, as it does not affect cyclone performance.

The internal geometry of a cyclone also has a great deal to do with its operating efficiency. The length and angle of the conical section (and the ratio of cone diameter to cone length), the size and shape of the feed inlet, the size of the vortex finder, and the size and adjustment means of the underflow opening all play important roles in a cyclone's effective separation of solids particles.

Operating efficiencies of cyclones may be measured in several different ways, but since the purpose of a cyclone is to discard maximum abrasive solids with minimum fluid loss, both solids and liquid aspects of removal must be considered. (A simple technique for comparing the efficiencies of two cyclones is given in Appendix B of this handbook.)

In a cyclone, larger particles have a higher probability of reporting to the bottom underflow (apex) opening, while smaller particles are more likely to report to the top (overflow) opening. The most common method of illustrating particle separation in cyclones is through a cut point curve.

Figure 3-22 shows the approximate cut point ranges for cyclones used with unweighted water-base

CONE SIZE (I.D.)

4"

5"

B"

8"

10"

12"

CUT POINT (MICRONS)

15-20/U

20-25jU

25-30jU

30-40jU

30-40jU

40-60jU

Figure 3-22 Hydrocyclone Capacities

Figure 3-22 Hydrocyclone Capacities mud and operated at 75 feet ±5 feet of inlet head.

Was this article helpful?

+1 -1

Post a comment