Canned Motor Pumps Canned Motor Pumps for the Conveying of Liquefied Gases — Alternative for High Pressure

Author / Editor: Dr. Günter Feldle / Dr. Jörg Kempf

More and more sealless canned motor pumps are being employed for the conveying of liquefied gases. They are distinguished by operational safety, an extremely low level of noise, low life cycle costs and in particular by the high degree of environmental friendliness, alongside their compactness and easy installation. They are a safe alternative to conventional centrifugal pumps and magnetic drive pumps.

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Schematic design of a canned motor pump
Schematic design of a canned motor pump
(Picture: Hermetic)

Liquefied gases are substances or mixtures of substances of which the critical temperature is below 50 °C or of which the vapour pressure lies above 200 kPa at 15 °C. Liquefied gases develop in the production of petrol and diesel fuel, for example butane and propane (LPG = liquefied petroleum gas). Other liquefied gases such as ethylene, propylene, ammonia, phosgene, chlorine, vinyl chloride and sulphur dioxide are intermediate products in the hydrocarbon processing industry (HPI). These gases liquefy under a slight positive pressure of around 800 kPa. In doing so, their volume decreases down to one 260th of the former value and can in this way be stored in tanks more easily.

Liquefied gases are not to be confused with liquefied natural gas (LNG). Natural gas is cleaned of nitrogen, carbon dioxide, noble gases and water in a desulphurisation plant. It cannot be designated as natural gas until the mixture consists of more than 90% methane at the end of the process. After the cleaning procedure, the mixture is cooled down to -162 °C. Methane changes its condition at this temperature, becoming liquid. The effect: natural gas decreases to one 600th of its former volume. In this way 600 m³ natural gas shrink to 1 m³ LNG.

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However many liquefied gases are hazardous, toxic, combustible, explosive, self-igniting, chemically unstable or corrosive. Consequently they should be conveyed in accordance with TA Luft, the German national implementation of the EU 96/61/EC directive via the integrated prevention and reduction of environmental pollution as well as the German Federal Pollution Control Act by means of the best available technology.