Vertically rotatable shaft assembly with thermally insulated housing

A vertically mountable shaft and bearing assembly for imparting rotary motion to a rotatable device submerged in a process fluid at high temperature, the assembly comprising:

• a shaft having a proximal end to which rotation can be imparted, and a distal end which is attached to the rotatable device;
• an upper mechanical bearing supporting the shaft near its proximal end;
• a lower mechanical bearing supporting the shaft near its distal end;
• a shaft housing that surrounds the lower mechanical bearing and a portion of the shaft proximal to the lower mechanical bearing, the shaft housing including a layer of thermal insulation proximal to an inward-facing surface of the shaft housing that inhibits conduction of heat from process fluid surrounding an exterior of the shaft housing into an interior of the shaft housing, the thermal insulation having a thermal conductivity below 1 W/(m° C.), the interior of the shaft housing being a reservoir containing a lubricant that lubricates the lower mechanical bearing;
• an upper seal that allows the proximal end of the shaft to rotatably extend beyond a proximal end of the shaft housing while isolating the shaft housing interior from a surrounding environment;
• a lower mechanical seal that allows the distal end of the shaft to rotatably extend beyond a distal end of the shaft housing while preventing entry of process fluid into the interior of the shaft housing when the distal end of the shaft housing is submerged in the process fluid;
• and
• a lubricant circulation system which is capable of circulating lubricant between the upper mechanical bearing, the lubricant reservoir within the shaft housing interior, the lower mechanical bearing, and a lubricant cooler external to the shaft housing.