Patent ID: 6912858

Claim:
A method of pumping a cryogenic liquid from a storage vessel comprising: removing a cryogenic liquid stream from said storage vessel; pumping at least a portion of the cryogenic liquid stream; prior to the pumping of the at least a portion of the cryogenic liquid stream, introducing the cryogenic liquid stream into a heat exchanger located in a phase separator and diverting a subsidiary cryogenic stream from the cryogenic liquid stream after passage of the cryogenic liquid stream through the heat exchanger; introducing the subsidiary cryogenic stream into the phase separator and subjecting the subsidiary cryogenic stream to a lower pressure than that of the storage vessel so as to cause the subsidiary cryogenic stream to boil and produce a boiling pool of a liquid fraction of the subsidiary cryogenic stream covering the heat exchanger and having a lower temperature than the cryogenic liquid stream, thereby to subcool the cryogenic liquid stream; and controlling flow of the subsidiary cryogenic stream by suspending the flow when the liquid fraction is at a predetermined level, above that of the heat exchanger, reestablishing the flow after liquid level of the liquid fraction has fallen due to the boil off thereof, and between the suspension of the flow and the reestablishment thereof, temporarily reestablishing the flow to remove warm and vaporized liquid.