Bearings, magnetic

Three types of bearings will be discussed oil-film bearings, rolling-element bearings (also known as antifriction bearings), and magnetic bearings. 

The rotordynamic study of a machine with magnetic bearings is quite different from the one of either oil-film or rolling-element bearings. The stiffness and damping properties of magnetic bearings can... 

Table 3-12 Turboexpanders with active magnetic bearings ...

This chapter discusses the most popular features and controls that are critical to turboexpander operations. Among those discussed are magnetic bearings, squeeze film dampers, radial fit bolts, valve arrangements for FCC expanders, FCC expander load shedding technology, and surge detection and avoidance. 

Reduced maintenance costs, leading to an overall improvement in system integrity and reliability. Tlie mean-times-between-failure for active magnetic bearings are equal to tliose of an electric motor. 

Improved rotor dynamic stability. The active magnetic bearing s ability to vary stiffness and damping permits rotation about the rotor s inertial axis, eliminating vibration and noise. 

In a radial active magnetic bearing, the rotor is held in position by electromagnets located on the stator (Figure 6-3). The rotor-to-stator position is constantly monitored by sensors that communicate with the electronic control system. If the rotor deviates from its position, the control system adjusts the current flow to the electromagnets to return the rotor back to its proper position. 

Active magnetic bearings are certainly suitable for turboexpanders. These bearings are now being used in the aerospace and machine-tool industries, as well as in a variety of both light and heavy industries. 

The active magnetic bearing s versatility allows it to be used in almost any rotating machine. Examples include compressors, blowers, pumps, turbines, centrifuges, x-ray tubes, vacuum pumps, spindles for... 

In 1985, the first active magnetic bearing in a pipeline compressor for continuous use was installed on the Alberta Gas Transmission System of NOVA Corporation. Tlie bearings have been running smoothly, with a noted improvement in compressor operation and efficiency. 

Rotor diameters, or quasi journals, include dimensions ranging from 14 mm (0.55 in.) to 600 mm (24 in.). Similarly, the load range accommodated by radial magnetic bearings is 0.3 N (0.007 lb) to 200 kN (45,000 lb). Rotational speeds range from a virtual standstill to as high as 800,000 rpm. 

CASE STUDIES ON ACTIVE MAGNETIC BEARINGS (AMB) AND DRY GAS SEALS (DGS) ... 

Magnetic Bearing Housing Sealing and Cooling Loop Control... 

In an offshore application the process gas flowing into a 3,600 kW turboexpander was compatible with the magnetic bearing material and a suitable seal gas source was available. This made it possible to use a pressurized bearing housing. 

Figure 6-7. Windage loss versus speed for pressurized and unpressurized magnetic bearing environments.

Temperature control of the magnetic bearing housing environment is critical to safe operation of turboexpanders. Atlas Copco-Rotoflow has developed several schemes to monitor the bearing housing temperature and maintain it at a safe level. 

The thrust capacity of a magnetic bearing is limited when compared to a conventional oil bearing. Simulation of potential upset conditions... 

Active Magnetic Bearings (AMB) and Dry Gas Seals (DGS) in Hydrocarbon Processing... 

In this case, details of turboexpander design with dry gas seals and active magnetic bearings are presented in enough detail that the application to this specific process is clarified. 

Turboexpanders with Active Magnetic Bearings Revisited. The... 

Agahi, R., Ershaghi, B., Bosen, W., and Leonhard, M., Turboexpanders with Magnetic Bearings in Air Separation and in Hazardous Areas, MAG 92, Alexandria, VA, 1992. 

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