Mounting and Sealing Molten Salt Pumps

    Understanding how to seal a molten salt pump to either a tank flange or a structure mounted above the tank is very critical for several reasons.
    First, because this seal area becomes part of the cool down transition section of the pump, it can grow into a major problem if not designed properly. Molten salt will climb the shaft and work its way into this seal area, solidifying and freezing up the rotating assembly if this area is too cool, or spraying dangerous molten salt outside of the tank to create an unsafe situation if it is too hot.
    This area can be 4-in to 6-in in long for tank mounted pumps, and as much as 4-ft to10-ft long for pumps mounted on structures above the tank. The shaft must be cooled down before the heat reaches the main thrust bearings. This seal area is the first cooling zone, but it must maintain a temperature just above the melting point of the salt.
    If molten salt is not stopped from migrating up the shaft prior to the first cooling zone, major failures can occur. The use of salt flingers and a counter flow screw machined into the main shaft will reduce the salt migration up the shaft. Based on the shaft speed and liquid levels in the tank, a secondary screw may be required. The size and design of the screws and flingers will vary based upon the temperatures and type of salt being used.
    In the second cooling zone, just above the seal area, heat fans are used to reduce the shaft temperature to 65-deg C before reaching the thrust bearings. The design of this area may require external fans for cooling the shaft if the pump sets idle for long periods of time.