Pumping cryogenic gases is no easy task. To liquefy this type of substance, the temperature must be lowered, and the system pressure increased. Cryogenic liquids are therefore different from “normal” liquids. Because they are processed at an extremely high system pressure, from 50 to 200 bar or more, and an extremely low temperature up to –200 °C. The viscosity is also extremely low (> 0.1 mPas); about a tenth of water. It is mainly the combination of these physical properties that makes it difficult.
For the pulsation-free pumping of cryogenic gases, depending on the desired differential pressure, both gear and turbine pumps are the perfect solution for these challenging applications.
The (shaft) sealing of the pump requires special attention. This is very difficult due to the extreme system pressure and temperature. A normal shaft seal (such as a gasket, lip seal, mechanical seal, etc.) is virtually impossible because it is blown out of the pump by the extreme pressure difference inside and outside the pump.
Magnetically coupled pumps
The pumps we offer for this application are equipped with a magnetic coupling with seals that are suitable for system pressures up to 325 barg and extremely low temperatures up to –200 °C. Due to the application of a magnetic coupling, there is no shaft seal, only static seals. As a result, the pump is hermetically closed and there is no risk of jams due to ice deposits. The materials of the seals must be especially resistant to extremely low temperatures, such as PTFE (= TEFLON®), FFPM (= Kalrez®) or metal (e.g. silver).
In order for the process to run smoothly, the pump and the pipes must be insulated to prevent ice build-up by moisture from outside.
SUURMOND offers three types of pumps that have been used for cryogenic applications. Two types of gear pumps and a turbine pump. The choice is determined by, among other things, the desired differential pressure, the required system pressure, and liquid temperature.
Examples of cryogen applications:
– Pumping of liquid nitrous oxide (N2O) as refrigerant
– Pumping of liquid carbon dioxide (CO2) as a refrigerant
– Pumping thermostatic fluids; ethylene glycol, silicone oils, etc.
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