Operating Experience

Multistage Boiler Feed Pump The multistage pump of Table 1 (refer to Figure 1) was installed as one of three otherwise identical pumps (two in parallel, one standby) in an electric utility generating plant (refer to Figure 2). The objective was to show that magnetic bearings would work in a typical field application of a pump of significant power level. This project took the first step of replacing the conventional bearings in this 610 hp (0.46 MW) eight stage centrifugal pump, which were outboard of the pump itself, and replacing them with heteropolar active magnetic bearings without any major design changes6. This was seen as the first of two steps, the second being a project where the bearings would be submerged in the operating fluid, allowing one seal system to be replaced8.

As with many magnetic bearing projects, the main lesson learned was that the transient bearing loads could not always be predicted ahead of time, and that the magnetic bearings gave very precise and important feedback of this information. Table 3 contains the design and field data. In this case, the 2500 lb (ii kN) transient load occurred when the plant underwent a suction pressure transient in which the available NPSH became so low that the first stage of this horizontally-opposed staging configuration (refer to Figure 1) apparently lost pressure rise completely6. The axial thrust of this stage was accordingly lost, destroying the intended axial hydrodynamic thrust balance of the pump. (See Sections 2.1 and 2.2.1.) Nevertheless, the conservative design of the thrust bearing enabled it to accommodate this load.

Single-Stage Process Pump The 800 hp (0.6 MW) single-stage double-suction process pump of size 8 X 26 (200mm X 660mm) of Table 1 was retrofitted with homopolar bearings7.

Closed-loop testing was conducted in the pump manufacturer's facility (see Figure 15). As indicated in Table 4, the results showed that a substantial operating margin exists for

TABLE 3 Operating experience with multistage pump
Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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