liquid is at the equilibrium temperature during this phase the valve v 2 a purge circuit 3 ensures continuous dilution of the impurities of the tank through the valve v 3 which sends the purge to the rich bottom liquid coming from the medium pressure column mp this rich liquid is then vaporized in the overhead condenser of the argon column ar this filling phase may be carried out by directly filling with high pressure liquid air 16 9 coming from the cold end of the main exchanger e 01 as illustrated or by taking a fluid from an intermediate point in the main exchanger in order to have a good equilibrium temperature of the final pressure of the tank or a subcooled fluid it will then be reheated by a bottom exchanger as described previously this device may also be applied to the cold boxes for separation by distillation of a mixture having as main components hydrogen and carbon monoxide in order to compensate for the drops in carbon monoxide content during the purification inversions it is possible to release a stream of carbon monoxide to the suction port of the carbon monoxide compressor or release the syngas stream in order to stabilize the gas supplies for the column for separating carbon monoxide and methane as the tank remains inside the cold box the risk of spreading liquid carbon monoxide is eliminated generally the invention may be applied to any cryogenic cold box preceded by a purification in order.