4
Mix Box Flow Analysis and Pump-Mixer Dynamics
The Flow conditions in both the lower and upper chambers
of the mix box calculate as turbulent. The hydrodynamic
loading conditions on the mix box structure were observed
to be highly variable and complex. See Figure 4.
Solution static pressures in a mixed condition for the
upper chamber and in unmixed conditions in the lower
chambers were calculated at a maximum of 5.13 psig on the
Aqueous side and 4.69 psig on the Organic side. Pressures
on the exterior walls and the bottom of the false floor in
the lower chamber are increased as solutions are forced up
through the semi-circles in the false floor, which have been
modeled as a modified orifice. In the calculation, the
traditional constitutive equation coefficient components
of the frictional and contraction orifice coefficients have
been modified to account for the sharp-edged semi-circle
together with the flat wall which bisects the circle through
the center. For the CAID design, and an orifice diameter
of 48,” pressures calculated at 0.0621 psig and 0.147 psig
on the Aqueous side at 7,800 gpm and 12,000 gpm respec-
tively and 0.0108 psig and 0.0319 psig on the Organic side
at 3,600 gpm and 6,200 gpm respectively. For the origi-
nal design of a 30” diameter orifice the initial calculation
resulted in an Aqueous side pressure of 0.409 psig.
Power draw information was taken in the field on 8
February 2012 for the E1B pump-mixer. The mixer cur-
rently has a Lightnin R301 impeller, 85-1/2” diameter
with six straight radial vanes. At approximately 40 amps,
the power consumption of the unit is around 38 hp. At
a noted Lightnin design lift of 3 ft. pumping efficiency is
around 22%, corroborated by the high specific speed of the
impeller at 1744. The ideal head development of the radial
vane impeller configuration calculates to 7.63 ft at 42 rpm
and ideal inlet conditions.
Additional information was available on the FMI-
Chino Operations E1B mixer where the mix box geometry
is similar to the Morenci E1B, but the mixer is a Lightnin
R320D, 64” diameter with six curved radial vanes. Data had
been taken at 56 rpm and 31 amps, giving approximately
30 hp. Impeller specific speed calculated to be 2512. The
ideal head development is 7.58 ft. at that speed. Morenci
also has the R320D impellers on site as uninstalled spares.
Fluid forces from impeller rotation were derived from
evaluating the velocity polygons between inlet and outlet of
the impeller.2 Pressure differentials and changes in momen-
tum from directional changes of the fluid were imparted
to the plate as distributed loads. The unbalanced force of
the solution stream coming from the R301 impeller and
impacting on the lower part of the upper chamber wall and
locally near the corner of the false floor is quite small and
calculates around 0.0611 psi at approximately 11,350 gpm
solution flows. The vane pass frequency for consideration
of fatigue loading at 42 rpm computed to 252 impulses
per minute or over 360,000 impulses per day. Therefore,
it would take 2.76 days to reach one million cycles. As the
vanes pass from the Aqueous side of the false floor orifice
to the Organic side the pass frequency is 42 impulses per
minute or over 60,000 impulses per day and
16.5 days to reach one million cycles. Due to the sig-
nificant velocity change that would happen near instan-
taneously as the impeller passes from the Aqueous side of
the false floor orifice to the Organic side, a high positive-
pressure impulse is likely to occur on the false floor plate
in the vicinity beneath the impeller. An opposite effect or
Figure 4. Typical turbulent solution surface in the E1B mix
box with R301 impeller
Figure 5. Typical semi-quiescent solution surface in the E2B
mix box with R320A impeller
Mix Box Flow Analysis and Pump-Mixer Dynamics
The Flow conditions in both the lower and upper chambers
of the mix box calculate as turbulent. The hydrodynamic
loading conditions on the mix box structure were observed
to be highly variable and complex. See Figure 4.
Solution static pressures in a mixed condition for the
upper chamber and in unmixed conditions in the lower
chambers were calculated at a maximum of 5.13 psig on the
Aqueous side and 4.69 psig on the Organic side. Pressures
on the exterior walls and the bottom of the false floor in
the lower chamber are increased as solutions are forced up
through the semi-circles in the false floor, which have been
modeled as a modified orifice. In the calculation, the
traditional constitutive equation coefficient components
of the frictional and contraction orifice coefficients have
been modified to account for the sharp-edged semi-circle
together with the flat wall which bisects the circle through
the center. For the CAID design, and an orifice diameter
of 48,” pressures calculated at 0.0621 psig and 0.147 psig
on the Aqueous side at 7,800 gpm and 12,000 gpm respec-
tively and 0.0108 psig and 0.0319 psig on the Organic side
at 3,600 gpm and 6,200 gpm respectively. For the origi-
nal design of a 30” diameter orifice the initial calculation
resulted in an Aqueous side pressure of 0.409 psig.
Power draw information was taken in the field on 8
February 2012 for the E1B pump-mixer. The mixer cur-
rently has a Lightnin R301 impeller, 85-1/2” diameter
with six straight radial vanes. At approximately 40 amps,
the power consumption of the unit is around 38 hp. At
a noted Lightnin design lift of 3 ft. pumping efficiency is
around 22%, corroborated by the high specific speed of the
impeller at 1744. The ideal head development of the radial
vane impeller configuration calculates to 7.63 ft at 42 rpm
and ideal inlet conditions.
Additional information was available on the FMI-
Chino Operations E1B mixer where the mix box geometry
is similar to the Morenci E1B, but the mixer is a Lightnin
R320D, 64” diameter with six curved radial vanes. Data had
been taken at 56 rpm and 31 amps, giving approximately
30 hp. Impeller specific speed calculated to be 2512. The
ideal head development is 7.58 ft. at that speed. Morenci
also has the R320D impellers on site as uninstalled spares.
Fluid forces from impeller rotation were derived from
evaluating the velocity polygons between inlet and outlet of
the impeller.2 Pressure differentials and changes in momen-
tum from directional changes of the fluid were imparted
to the plate as distributed loads. The unbalanced force of
the solution stream coming from the R301 impeller and
impacting on the lower part of the upper chamber wall and
locally near the corner of the false floor is quite small and
calculates around 0.0611 psi at approximately 11,350 gpm
solution flows. The vane pass frequency for consideration
of fatigue loading at 42 rpm computed to 252 impulses
per minute or over 360,000 impulses per day. Therefore,
it would take 2.76 days to reach one million cycles. As the
vanes pass from the Aqueous side of the false floor orifice
to the Organic side the pass frequency is 42 impulses per
minute or over 60,000 impulses per day and
16.5 days to reach one million cycles. Due to the sig-
nificant velocity change that would happen near instan-
taneously as the impeller passes from the Aqueous side of
the false floor orifice to the Organic side, a high positive-
pressure impulse is likely to occur on the false floor plate
in the vicinity beneath the impeller. An opposite effect or
Figure 4. Typical turbulent solution surface in the E1B mix
box with R301 impeller
Figure 5. Typical semi-quiescent solution surface in the E2B
mix box with R320A impeller