This invention relates to a process for the liquefaction of gases, for example, helium, and especially to a process wherein impurities are frozen out, first in a freeze purification system, and removed from the gas; then the purified gas is liquefied in a refrigerating unit. The freeze purification system, in an alternating sequence of purification phases and regeneration phases, is alternately brought into thermal contact with cold gas and hot gas from the refrigerating unit and in each purification phase a part of the purified gas is stored in a medium-pressure buffer vessel at a pressure of P.sub.M, while in each regeneration phase, a part of the gas stored in the medium-pressure buffer vessel is liquefied.
Gases, which are to be liquefied in a refrigerating unit, for example in a helium cryostat, must be freed beforehand of impurities, which could otherwise lead to "icing" of the equipment parts of the refrigerating unit. It is known, for example, from DKV-Tagungsbericht [German Refrigerating Society, Proceedings], vol. 8 (1981), pages 101-118, to remove air impurities from crude helium by condensing and freezing, before the purified helium is liquefied in a refrigerating unit. For the purification of the crude helium, there is employed a freeze purification system comprised of heat exchangers and a separator.
In the heat exchangers, the crude helium is brought into indirect thermal contact with cold gas from the refrigerating unit so that the air impurities are condensed as liquids and then residual air impurities are frozen out as solids from the crude helium. Condensed liquid air is carried off from the separator to the atmosphere. Since the heat exchangers become iced in time by frozen-out air components, the freeze purification system has to be regularly regenerated. For this purpose, warm gas from the refrigerating unit is conducted countercurrently through the freeze purification system. Since during the regeneration phase, an amount of pure helium must be liquefied for the process to run continuously, this extra amount has to be produced and stored during the purification phase. This intermediate storage takes place in a medium-pressure buffer vessel at a pressure P.sub.M.