Chemistry Reference
In-Depth Information
two sheets of metal that extend from one side of the rotor to the other. They also
extend the full length of the separating zone (see Figure 10.5) and force the enter-
ing liquid to immediately attain the full rotational speed of the rotor and stay at that
speed. Thus, the dispersion experiences the full centrifugal force of the contactor for
the entire time it is in the rotor. A small weep hole at the bottom outer edge of each
vane allows the liquid surface in the various quadrants to be at the same radius for
a given height. Near the bottom of the separating zone, a horizontal disk, called a
“diverter disk,” is embedded in the vertical vanes. This disk extends into the middle
of the separating zone, thus forcing all of the dispersion into a region of higher cen-
trifugal force. The center of the disk is open so that entrained air can move up to
the LW and escape over that weir. This design prevents pressurization of the lower
region of the rotor, which would reduce liquid flow into the rotor. The vertical vanes
next to the LW can extend into the center of the rotor or can stop at the edge of the
weir. While both designs work, each design gives a slightly different weir coefficient
(Leonard et al., 1980b). For a given rotor design, one needs to specify this design
parameter and then use it consistently so that all the rotors perform the same.
The route for the less-dense phase leaving the rotor is fairly simple. When the
separated less-dense phase flows inward and up over the LW, the liquid is thrown out
into a channel (like a rain gutter) and moves to one of four sets of exit channels, one
in each quadrant of the rotor. Each set of channels consists of a series of holes or a
single rectangular channel that allows the less-dense phase to be flung by the rotor
into the lower collector ring.
The route for the more-dense phase is more complex. The separated more-dense
phase flows outward and up into the underflow. Each of the four sets of underflow
channels is either a series of drilled holes (see Figure 10.3) or a slot. Each quadrant of
the rotor has one set of underflow channels between the four sets of exit channels for
the less-dense phase. At the exit of each underflow channel is a riser that carries the
more-dense-phase liquid inward up to the upper weir. This riser is created when the
top plate is placed on the rotor, shown in Figure 10.6. In the SRL and ANL contac-
tors, the riser is narrow so that it will carry out fine particles that might be entrained
in the more-dense phase. In the CINC contactor, the underflow channel is very short;
thus, the riser to the upper weir is very wide, so that entrained particles have little
possibility of being carried out in the more-dense phase. This design may not prove
problemmatic. The particles could settle out and create a narrow riser channel to the
upper weir, which then carries out any additional particles. When the more-dense
phase reaches the upper weir, it flows up over the weir and is spun out. In some
contactors, the rotor is open above the upper weir, and the liquid is thrown out into
the upper collector ring, as shown in Figure 10.1. Other contactors have a cover over
the upper weir. The liquid is thrown out into a channel (again, like a rain gutter) and
moves to one of four sets of exit channels, one in each quadrant of the rotor. Each set
of channels consists of a series of holes or a single rectangular channel (see upper
rectangular openings in Figure 10.5), which allows the more-dense phase to be flung
by the rotor into the upper collector ring.
Just as contactors typically have four vertical vanes in the separating zone, they
also have four vertical vanes in the riser to the upper weir. Also, these vanes can stop
at the edge of the upper weir or continue on to the center of the rotor. Typically, these
