Cryogenic storage tank with a retrofitted in-tank cryogenic pump

Abstract

A removable pump assembly for use in a cryogenic storage tank pumps liquid cryogen directly from the primary storage container with low boiloff loss. The cryogenic storage tank has an outer vessel, an inner vessel, an evacuated insulation space therebetween and a access port connecting the inner and outer vessels and providing an open cylindrical access to the interior of the cryogenic tank. A pump mounting tube assembly is disposed into the interior of the inner vessel of the cryogenic tank through the access port and includes an inner pump mounting tube and an outer pump mounting tube which are joined at their upper and lower rims to define an insulating jacket between the two tubes. The inner and outer pump mounting tubes are affixed at their upper ends to a top and bottom plate. The top and bottom plate in turn is affixed to an insulating block. Only the insulating block, which is disposed in the access port of the cryogenic tube, is in contact with any portion of the cryogenic tank. The insulating block provides a poor thermal path and also provides a gas seal between the pump mounting tube and the access port of the cryogenic tank. The pump mounting tube thus defines a long heat path into the cryogenic tank and is insulated from the liquid cryogen by a pocket of trapped gas formed within the inner tube by heating cryogen. A pump is introduced through the inner pump mounting tube and is also insulated against contact with liquid cryogen by the trapped gas. Only the lowermost end of the pump is immersed in cryogen, thereby minimizing heat conduction into the cryogen within the tank.