According to Stokes Law, particle setting velocity is proportional to G-force. Since G-force increases with the square of bowl RPM, it is an important parameter of decanting centrifuge performance. G-force also increases linearly with bowl diameter. Figure 1 shows how solids removal efficiency improves with increasing G-force. For a given particle size and fluid properties, there is a minimum G-force necessary to invoke settling. Although high G-force is desirable, the cost is proportional to the cube of the bowl rpm and there are similar economic limitations on bowl diameter as well. Thus, the required G- force must be obtained from a practical combination of speed and diameter. Most oilfield decanting centrifuges have bowl dimensions from 14 to 28 inches in diameter and lengths from 30 to 55 in. Rotational speeds range from 1000 rpm to 4000 rpm, depending on the application. The more expensive, high “G” machines can provide up to 3,000 G’s.

Effect of G-Force on Separation (Higher G's Improve Separation Performance)

Note: however, that increasing G-force eventually reduces solids conveyance capacity due to torque limitations. As G-force increases, more solids are settled in the bowl and they adhere more tightly. More conveyor or torque is required to move the solids out. Once the torque limitations of the machine are reached, conveyance ceases.
G-Force for a Decanting centrifuges:
G’s = RPM2 x .0000142 x Diameter of Bowl (in inches)

High G-force decanting centrifuges are available from GN Solids Control.

The decanter centrifuge is used in weighted mud applications to recover valuable weighting material from mud which must be discharged due to unacceptable colloidal solids content. The decanter centrifuge settles out barite and coarse drilled solids which are returned to the active mud system to maintain density. The relatively clean centrate containing liquid and colloidal solids is discarded. These colloidal solids cause many drilling fluid problems, such as high surge/swab pressures and ECD, differential sticking and high chemical costs. Usually the value of the weighting agent in these mud systems makes it economic to recover the weighting agent from the whole mud before it is discarded.Ideally, the barite recovery process should remove only colloidal solids without losing the larger particle sizes used as weighting material.

Discarding potentially reusable barite increases barite use and drilling fluid cost. Barite losses can be reduced when the centrifuge makes the maximum liquid/solids separation. As discussed in the previous section, this means operating the decanter centrifuge at high G-force.

Cutting-edge research and product development is the soul of GN. Through trial and error, GN new generation decanter centrifuges finally come out. The mechanical design and electric control system are updated to a new high level.

Compact Mechanical Design

The primary motor and the secondary motor set at the one side and leave much room for operator to get access to rotating assembly. Collection box cover supporting system is installed with which much labor can be saved when opening the collection box and doing the maintenance.

VFD PLC Control Panel

In addition to the normal VFD (Variable Frequency Drive) Centrifuge. GN also developed DECANTER CENTRIFUGE controlled and monitored by a Programmable Logic Controller (PLC). Compared to other centrifuges, it requires fewer operating personnel and features automatic adjustment for different operating conditions.

GN decanter centrifuge was shown at Colombia Oil and Gas 2013 (XV Congreso Colombiano de Petróleo y Gas 2013). This provides a good chance for Latin America customers to take a close look at GN efficient centrifuge.

GN Decanter Centrifuge at Colombia Oil and Gas 2013