Linde Kryotechnik can reflect on decades of experience in the construction of helium liquefiers. In all probability, the helium that is captured in natural gas fields will be liquefied in a Linde Kryotechnik system. A liquefier is an open system which produces a liquid output and requires an equivalent quantity of feed gas as input. The mass flow rates involved in this process are asymmetric.

Depending on the requirements and specific application, Linde Kryotechnik offers a range of standard and special systems for helium liquefaction. The liquid helium output of Linde systems ranges from 14 to well over 3500 litres per hour in a single cold box.

Standard systems
For universities and research institutes with a liquid helium requirement of 14 to 280 l/h, Linde Kryotechnik has developed the standard systems of the L70, L140 and L280 series. The wide range of performance ratings is achieved by using different compressors and precooling with or without liquid nitrogen. Integrated into the cold box is a freeze-out purifier to remove contaminants from the helium. All standard systems are fitted with a Siemens S-7-300 automatic control and monitoring system. A PC system is offered for visualization; it can be fitted with integrated remote control via modem.

Special systems
For gas producers who market helium worldwide, as well as research institutes with helium requirements in excess of the standard ratings, Linde Kryotechnik has developed a series of special systems with a liquid helium output ranging from 250 to well over 3500 l/h. In bulk liquefiers, contaminants are removed from the helium prior to liquefaction in separate components where cryogenic, physical or chemical processes are used for accumulation/liquefaction of contaminants and for adsorption under pressure variation.

The main components of a helium liquefier are:

• oil-injection screw compressors
• vacuum-insulated cold box
• aluminium-plate heat exchanger
• gas-bearing expansion turbines
• liquid storage tank
• control system

Further system components such as:

• raw gas compressors
• purification systems
• storage tanks and filling devices
• helium recovery

are designed, supplied and installed by Linde Kryotechnik.