Chemistry Reference
In-Depth Information
air-controlled weir. However, these spindles are expensive and have a long delivery
time. More recent contactors were designed with the diameter of the upper weir set
so that an air-controlled weir was not required (Leonard, 1983). These contactors can
use inexpensive off-the-shelf motors. For contactors larger than 4 cm, motors already
designed to operate in a corrosive environment are commercially available. For high
radiation environments, the motors must have electrical insulation and bearing lubri-
cant that can stand up to radiation, which will increase the motor cost.
A key feature of all contactor designs used in high radiation environments is the
ability to remove and replace the motor/rotor assembly easily by using remote main-
tenance tools. A typical design for a unit that is 4 cm or smaller has two nuts at the
top of the motor/rotor assembly holding it in place (see Figure 10.17 and Leonard et
al. (1997)). For larger units, additional nuts may be required. In all cases, the nuts
are designed to be attached and removed remotely. An air-powered torque wrench is
used to unscrew the nuts. A hook at the top of the motor/rotor assembly and tapered
guide pins of unequal height allow the assembly to be removed and reinserted easily
by using an overhead crane.
While some CINC units have a bearing at the bottom of the rotor, it is now being
eliminated whenever possible. The bottom bearing is very expensive, hard to replace,
and, if the contactor runs dry, cannot be lubricated and will thus, fail. In a production
contactor, the bearing noise should be monitored so that bearing problems can be
identified and corrected before the bearing fails.
In all CINC contactors and the latest ANL contactor (a 15-cm unit that has been
designed but not yet built), the motor rotor and the contactor rotor are isolated from
each other with respect to their vibrations. This separation is accomplished by means
FIGURe 10.17
Eight-stage 4-cm centrifugal contactor with face-mounted motors.
