An automatic helium purifier for integration with small laboratory liquefiers

It is now customary for the helium boil-off gas from experimental cryogenic liquefiers to be collected and returned to the central liquefaction facility. Unfortunately this gas becomes heavily contaminated with considerable quantities of air. This paper deals with the design and development of a fully automatic helium purifier which is capable of successfully reducing the level of impurity to that suitable for continuous operation of the liquefier. Air removal is by means of a liquefaction stage with automatic drain followed by a solidification stage. During recycling the latter is liquefied and drained back to the liquification stage where it is also drained. The refrigeration for the cycle at 20 K and 90 K is obtained from side streams of a standard laboratory liquefier. Field experience has shown that the system is capable of handling any concentration of air impurity without contaminating the process stream of the plant. (author)