Principles and Basic Concepts of Cryogenic Pumps

     Basic Concepts of Cryogenic Pumps

Typically, the temperature of the medium conveyed by cryogenic pumps ranges from -30°C for relatively higher-temperature applications down to -220°C for ultra-low-temperature scenarios. During the design phase, factors such as the low-temperature performance and impact resistance (primarily indicated by the Ak value) of materials, as well as the physical and chemical properties of the medium, must be taken into account—especially the high volatility of media like liquid oxygen, liquid nitrogen, liquid argon, and liquefied natural gas (LNG). The seal structure of the pump is designed based on these properties. Most cryogenic pumps adopt packing seals, which offer a cost-effective sealing solution.

Cryogenic pumps are specialized pumps used in petroleum and chemical plants to transfer liquid hydrocarbons, liquefied natural gas, as well as liquefied gases such as liquid oxygen and liquid nitrogen in refrigeration systems. For this reason, they are also referred to as cryopumps.

Types of Cryogenic Pumps

A. Piston and Plunger Pumps

These types of pumps are generally used for gas filling and in chemical processes (e.g., injecting high-pressure nitrogen, nitrogen dioxide, carbon dioxide, etc., into chemical reactors), as well as in metallurgical engineering (e.g., delivering gas into steelmaking furnaces in steel mills). As transfer pumps, they typically have a smaller flow rate compared to centrifugal pumps, but can effectively provide high gas delivery pressure.

B. Centrifugal Pumps

Centrifugal cryogenic liquid pumps are commonly used to transfer cryogenic liquids from one cryogenic storage vessel to another, or as process pumps in air separation units (for large flow rate applications). These pumps usually employ mechanical seals or labyrinth seals, which entail higher sealing costs.