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Solar Thermal Power Stations

Solar Thermal Power Stations Are a Prime Application for Canned Motor Pumps

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EDL Anlagenbau Gesellschaft mbH
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The main advantages of canned motor pumps are:

  • Double safety containment: even in the unlikely event that the stator can ruptures, fluid is still contained by the outer casing, so the pump is 100% leak-free.
  • No mechanical seals: eliminating seals, which are subject to wear and tear, increases mean time between failures (MTBF) by a factor of 3–4, leading to fewer shutdowns and lower maintenance costs.
  • No seal support system: sealless design and product-lubricated bearings mean no expensive cooling or lubrication systems to install and maintain.
  • No coupling: the close-coupled design eliminates the need for a coupling and for shaft alignment — and often a complicated baseplate too.
  • Low noise: with no couplings, exposed motor bearings or cooling fans, noise levels are far below those of conventional and mag-drive pumps.

Extra cooling for the motor

A canned motor pump operating at high temperatures typically requires extra cooling for the motor. This can be done by fitting an auxiliary impeller to recirculate the fluid in the rotor cavity through an external heat exchanger, which can be mounted either around the motor or separately (Fig. 2). As a result, the temperature of the secondary cooling/lubricating circuit remains in the range 60–80 °C even when that of the pumped fluid is as high as 450 °C. This allows the motor windings to be manufactured to insulation Class H, which is robust and long-lived.

The impeller housing is separated from the canned motor by a relatively long, narrow, circumferential gap. This acts as a thermal barrier by equalizing the pressure differential between the hydraulics and the rotor cavity, so that there is very little interchange of fluid between the two sections. Without this separation, cooling the fluid passing through the motor would result in unacceptably high energy losses.

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