ELECTRIC MOTORS FOR CENTRIFUGAL PUMP AND CENTRIFUGE

Electric Motors For Decanter Centrifuge

Most Decanter Centrifuges use the same NEMA design B explosion-proof motors used for centrifugal pumps: either 1500 rpm at 50 Hz or 1800 rpm at 60 Hz. Decanter Centrifuges may draw up to seven times the full-load current for approximately 15 seconds at startup. It is considered good practice to limit centrifuge startups to two starts per hour to protect the motor because the current draw closely approaches the limit.

Oilfield centrifuges do not always use a direct drive between the motor and centrifuge. Direct drive requires expensive, variable-speed motors that have restricted availability of replacement parts and repair facilities. Most oilfield centrifuges are connected to the motor by a fluid clutch or a hydraulic drive, which uses a system of adding or subtracting motor or hydraulic oil to increase/decrease slippage between the driver and driven coupling halves. Some centrifuges use a variable-speed electric motor startup system that brings the centrifuge slowly up to operational rotating speed. It is important that all personnel understand the manufacturer’s recommended startup and shutdown procedures.

Early centrifuges were capable of generating 500 to perhaps 1500 g’s of acceleration. Today, machines commonly generate 2000 to 3000 g’s. The advent of higher g centrifuges is attributed to improvements in bearing design and manufacturing procedures, including hard surfacing with tungsten carbide and precision robot welding.

Eletric Motors for Centrigual Pumps

The fluid volume necessary to be moved by many centrifugal pumps is related to the rig circulation rate and the specific rig plumbing. Centrifugal pumps should be sized by the particular application and the maximum anticipated flow rate. Piping friction losses—if lines are reasonably short, with few turns or restrictions, and flow velocities between 5 and 10 feet per second—are readily estimated. The pressure, or head, which should be delivered to each piece of equipment (for hydrocyclones, typically 75 feet of head) is specified by the equipment manufacturer.

Horsepower requirements for centrifugal pumps, when pumping water or fluids of water-like viscosity, are well established and published with the performance curve for each design. See Chapter 18 on centrifugal pumps.