PURPOSE: To separate vapor from liquid well and permit to supply refrigerant, containing little vapor phase contents, to a cooling section by a method wherein a partitioning plate is provided between the outlet port of a pipeline, returning from the cryo-cooling section connected to the upper part of the vapor-liquid separator, and the level of the refrigerant liquid in the vapor- liquid separator.

CONSTITUTION: In order not to mix the refrigerant, reserved in the vapor-liquid separator 1 and containing little vapor phase contents, directly with the refrigerant, coming from the cryo- cooling section 3 and containing much vapor phase contents, the outlet port of the pipeline 4, returning from the cryo-cooling section 3, is connected to the upper part of the vapor-liquid separator 1. In order to separate vapor and liquid of the refrigerant, introduced from the returning pipeline 4 and containing much vapor phase contents, under the stationary operation of the cryo-cooling section 3 and reserve only the liquid phase contents in the vapor-liquid separator 1, the partitioning plate 7 is provided between the outlet port of the returning pipeline 4 and the level of the liquid upon the stationary operation. The outlet port of the refrigerant, supplied from a supplying pipeline 6 into the vapor-liquid separator 1, is connected to a position between the partitioning plate 7 and the level of the liquid upon the stabilized operation. According to this method, the direct mixing of the refrigerant, supplied from the supplying pipeline 6, through which the liquid and vapor phases of the refrigerant are mixed, into the vapor-liquid separator may be prevented.